diff --git a/swad_centre.c b/swad_centre.c
index 19513108b..03b75ec19 100644
--- a/swad_centre.c
+++ b/swad_centre.c
@@ -416,7 +416,8 @@ static void Ctr_ListOneCentreForSeeing (struct Centre *Ctr,unsigned NumCtr)
 
    /***** Number of users in courses of this centre *****/
    HTM_TD_Begin ("class=\"%s RM %s\"",TxtClassNormal,BgColor);
-   HTM_Unsigned (Ctr->NumUsrs);
+   HTM_Unsigned (Usr_GetNumUsrsInCrssOfCtr (Rol_UNK,		// Here Rol_UNK means "all users"
+					    Ctr->CtrCod));
    HTM_TD_End ();
 
    /***** Centre status *****/
@@ -612,9 +613,6 @@ void Ctr_GetListCentres (long InsCod)
 
          /* Get number of courses in this centre */
          Ctr->NumCrss = Crs_GetNumCrssInCtr (Ctr->CtrCod);
-
-	 /* Get number of users in courses of this centre */
-	 Ctr->NumUsrs = Usr_GetNumUsrsInCrssOfCtr (Rol_UNK,Ctr->CtrCod);	// Here Rol_UNK means "all users"
         }
      }
    else
@@ -647,7 +645,6 @@ bool Ctr_GetDataOfCentreByCod (struct Centre *Ctr,
    Ctr->NumUsrsWhoClaimToBelongToCtr = 0;
    Ctr->Degs.Num =
    Ctr->NumCrss  = 0;
-   Ctr->NumUsrs  = 0;
 
    /***** Check if centre code is correct *****/
    if (Ctr->CtrCod > 0)
@@ -704,9 +701,6 @@ bool Ctr_GetDataOfCentreByCod (struct Centre *Ctr,
 
 	    /* Get number of courses in this centre */
 	    Ctr->NumCrss = Crs_GetNumCrssInCtr (Ctr->CtrCod);
-
-	    /* Get number of users in courses of this centre */
-	    Ctr->NumUsrs = Usr_GetNumUsrsInCrssOfCtr (Rol_UNK,Ctr->CtrCod);	// Here Rol_UNK means "all users"
 	   }
 
          /* Set return value */
@@ -944,12 +938,16 @@ static void Ctr_ListCentresForEdition (void)
       /* Put icon to remove centre */
       HTM_TR_Begin (NULL);
       HTM_TD_Begin ("class=\"BM\"");
-      if (Ctr->Degs.Num ||
-	  Ctr->NumUsrsWhoClaimToBelongToCtr ||
-	  Ctr->NumUsrs ||	// Centre has degrees or users ==> deletion forbidden
-          !ICanEdit)
+      if (!ICanEdit)
 	 Ico_PutIconRemovalNotAllowed ();
-      else
+      else if (Ctr->Degs.Num)				// Centre has degrees
+	 Ico_PutIconRemovalNotAllowed ();
+      else if (Ctr->NumUsrsWhoClaimToBelongToCtr)	// Centre has users who claim to belong to it
+	 Ico_PutIconRemovalNotAllowed ();
+      else if (Usr_GetNumUsrsInCrssOfCtr (Rol_UNK,	// Here Rol_UNK means "all users"
+					  Ctr->CtrCod))	// Centre has users
+	 Ico_PutIconRemovalNotAllowed ();
+      else						// I can remove centre
         {
          Frm_StartForm (ActRemCtr);
          Ctr_PutParamOtherCtrCod (Ctr->CtrCod);
@@ -1059,7 +1057,8 @@ static void Ctr_ListCentresForEdition (void)
 
       /* Number of users in courses of this centre */
       HTM_TD_Begin ("class=\"DAT RM\"");
-      HTM_Unsigned (Ctr->NumUsrs);
+      HTM_Unsigned (Usr_GetNumUsrsInCrssOfCtr (Rol_UNK,		// Here Rol_UNK means "all users"
+					       Ctr->CtrCod));
       HTM_TD_End ();
 
       /* Centre requester */
@@ -1210,11 +1209,14 @@ void Ctr_RemoveCentre (void)
    Ctr_GetDataOfCentreByCod (Ctr_EditingCtr,Ctr_GET_EXTRA_DATA);
 
    /***** Check if this centre has teachers *****/
-   if (Ctr_EditingCtr->Degs.Num ||
-       Ctr_EditingCtr->NumUsrsWhoClaimToBelongToCtr ||
-       Ctr_EditingCtr->NumUsrs)	// Centre has degrees or users ==> don't remove
+   if (Ctr_EditingCtr->Degs.Num)				// Centre has degrees
       Ale_ShowAlert (Ale_WARNING,Txt_To_remove_a_centre_you_must_first_remove_all_degrees_and_teachers_in_the_centre);
-   else	// Centre has no teachers ==> remove it
+   else if (Ctr_EditingCtr->NumUsrsWhoClaimToBelongToCtr)	// Centre has users who claim to belong to it
+      Ale_ShowAlert (Ale_WARNING,Txt_To_remove_a_centre_you_must_first_remove_all_degrees_and_teachers_in_the_centre);
+   else if (Usr_GetNumUsrsInCrssOfCtr (Rol_UNK,			// Here Rol_UNK means "all users"
+				       Ctr_EditingCtr->CtrCod))	// Centre has users
+      Ale_ShowAlert (Ale_WARNING,Txt_To_remove_a_centre_you_must_first_remove_all_degrees_and_teachers_in_the_centre);
+   else	// Centre has no degrees or users ==> remove it
      {
       /***** Remove all the threads and posts in forums of the centre *****/
       For_RemoveForums (Hie_CTR,Ctr_EditingCtr->CtrCod);
@@ -1241,6 +1243,9 @@ void Ctr_RemoveCentre (void)
 		      "DELETE FROM centres WHERE CtrCod=%ld",
 		      Ctr_EditingCtr->CtrCod);
 
+      /***** Flush caches *****/
+      Ctr_FlushCacheNumUsrsInCrssOfCtr ();
+
       /***** Write message to show the change made *****/
       Ale_CreateAlert (Ale_SUCCESS,NULL,
 	               Txt_Centre_X_removed,
@@ -2052,7 +2057,6 @@ static void Ctr_EditingCentreConstructor (void)
    Ctr_EditingCtr->Degs.Num        = 0;
    Ctr_EditingCtr->Degs.Lst        = NULL;
    Ctr_EditingCtr->NumCrss         = 0;
-   Ctr_EditingCtr->NumUsrs         = 0;
    Ctr_EditingCtr->NumUsrsWhoClaimToBelongToCtr = 0;
   }
 
diff --git a/swad_centre.h b/swad_centre.h
index 8003a64f8..557284646 100644
--- a/swad_centre.h
+++ b/swad_centre.h
@@ -73,7 +73,6 @@ struct Centre
    char WWW[Cns_MAX_BYTES_WWW + 1];
    struct ListDegrees Degs;	// List of degrees in this centre
    unsigned NumCrss;		// Number of courses in this centre
-   unsigned NumUsrs;		// Number of users in courses of this centre
    unsigned NumUsrsWhoClaimToBelongToCtr;	// Number of users who claim to belong in this centre
   };
 
diff --git a/swad_changelog.h b/swad_changelog.h
index 62e4a29bf..a117a932e 100644
--- a/swad_changelog.h
+++ b/swad_changelog.h
@@ -492,7 +492,7 @@ enscript -2 --landscape --color --file-align=2 --highlight --line-numbers -o - *
 En OpenSWAD:
 ps2pdf source.ps destination.pdf
 */
-#define Log_PLATFORM_VERSION	"SWAD 19.112.3 (2020-01-04)"
+#define Log_PLATFORM_VERSION	"SWAD 19.112.4 (2020-01-05)"
 #define CSS_FILE		"swad19.112.css"
 #define JS_FILE			"swad19.91.1.js"
 /*
@@ -501,6 +501,7 @@ ps2pdf source.ps destination.pdf
 // TODO: No se puede entrar con DNI '1' suponiendo que no tenga password ¿por qué?
 // TODO: Mapas más estrechos en móvil
 
+	Version 19.112.4: Jan 05, 2020	Optimization in number of users in courses of a centre. (278385 lines)
 	Version 19.112.3: Jan 04, 2020	Fixed bug in hierarchy. (278357 lines)
 	Version 19.112.2: Jan 04, 2020	Changing action descriptions from database to swad-core. Not finished. (278351 lines)
 	Version 19.112.1: Jan 03, 2020	Code refactoring in maps. (278391 lines)
diff --git a/swad_global.c b/swad_global.c
index 9599b971a..5b02ee6de 100644
--- a/swad_global.c
+++ b/swad_global.c
@@ -412,6 +412,7 @@ void Gbl_InitializeGlobals (void)
    Cty_FlushCacheCountryName ();
    Ins_FlushCacheShortNameOfInstitution ();
    Ins_FlushCacheFullNameAndCtyOfInstitution ();
+   Ctr_FlushCacheNumUsrsInCrssOfCtr ();
    Usr_FlushCacheUsrIsSuperuser ();
    Usr_FlushCacheUsrBelongsToIns ();
    Usr_FlushCacheUsrBelongsToCtr ();
diff --git a/swad_global.h b/swad_global.h
index baba4ca02..da849e297 100644
--- a/swad_global.h
+++ b/swad_global.h
@@ -772,6 +772,12 @@ struct Globals
 	 char ShrtName[Hie_MAX_BYTES_SHRT_NAME + 1];
 	 char CtyName[Hie_MAX_BYTES_FULL_NAME + 1];
 	} InstitutionShrtNameAndCty;
+      struct
+        {
+	 Rol_Role_t Role;
+	 long CtrCod;
+	 unsigned NumUsrs;
+        } NumUsrsInCrssOfCtr;
       struct
 	{
 	 long UsrCod;
diff --git a/swad_user.c b/swad_user.c
index 0e29d62d1..7db6b7005 100644
--- a/swad_user.c
+++ b/swad_user.c
@@ -4200,13 +4200,30 @@ unsigned Usr_GetNumUsrsInCrssOfDeg (Rol_Role_t Role,long DegCod)
 /*****************************************************************************/
 // Here Rol_UNK means any user (students, non-editing teachers or teachers)
 
+void Ctr_FlushCacheNumUsrsInCrssOfCtr (void)
+  {
+   Gbl.Cache.NumUsrsInCrssOfCtr.Role    = Rol_UNK;
+   Gbl.Cache.NumUsrsInCrssOfCtr.CtrCod  = -1L;
+   Gbl.Cache.NumUsrsInCrssOfCtr.NumUsrs = 0;
+  }
+
 unsigned Usr_GetNumUsrsInCrssOfCtr (Rol_Role_t Role,long CtrCod)
   {
-   unsigned NumUsrs;
+   /***** 1. Fast check: Trivial case *****/
+   if (CtrCod <= 0)
+      return 0;
 
-   /***** Get the number of users in courses of a centre from database ******/
+   /***** 2. Fast check: If cached... *****/
+   if (Role == Gbl.Cache.NumUsrsInCrssOfCtr.Role &&
+       CtrCod == Gbl.Cache.NumUsrsInCrssOfCtr.CtrCod)
+      return Gbl.Cache.NumUsrsInCrssOfCtr.NumUsrs;
+
+   /***** 3. Slow: get number of users in courses of a centre
+                   from database *****/
+   Gbl.Cache.NumUsrsInCrssOfCtr.Role   = Role;
+   Gbl.Cache.NumUsrsInCrssOfCtr.CtrCod = CtrCod;
    if (Role == Rol_UNK)	// Any user
-      NumUsrs =
+      Gbl.Cache.NumUsrsInCrssOfCtr.NumUsrs =
       (unsigned) DB_QueryCOUNT ("can not get the number of users"
 				" in courses of a centre",
 				"SELECT COUNT(DISTINCT crs_usr.UsrCod)"
@@ -4218,7 +4235,7 @@ unsigned Usr_GetNumUsrsInCrssOfCtr (Rol_Role_t Role,long CtrCod)
    else
       // This query is very slow.
       // It's a bad idea to get number of teachers or students for a big list of centres
-      NumUsrs =
+      Gbl.Cache.NumUsrsInCrssOfCtr.NumUsrs =
       (unsigned) DB_QueryCOUNT ("can not get the number of users"
 				" in courses of a centre",
 				"SELECT COUNT(DISTINCT crs_usr.UsrCod)"
@@ -4228,7 +4245,7 @@ unsigned Usr_GetNumUsrsInCrssOfCtr (Rol_Role_t Role,long CtrCod)
 				" AND courses.CrsCod=crs_usr.CrsCod"
 				" AND crs_usr.Role=%u",
 				CtrCod,(unsigned) Role);
-   return NumUsrs;
+   return Gbl.Cache.NumUsrsInCrssOfCtr.NumUsrs;
   }
 
 /*****************************************************************************/
diff --git a/swad_user.h b/swad_user.h
index 2fdc274c8..432202890 100644
--- a/swad_user.h
+++ b/swad_user.h
@@ -409,6 +409,7 @@ void Usr_WriteRowUsrMainData (unsigned NumUsr,struct UsrData *UsrDat,
 
 unsigned Usr_GetNumUsrsInCrs (Rol_Role_t Role,long CrsCod);
 unsigned Usr_GetNumUsrsInCrssOfDeg (Rol_Role_t Role,long DegCod);
+void Ctr_FlushCacheNumUsrsInCrssOfCtr (void);
 unsigned Usr_GetNumUsrsInCrssOfCtr (Rol_Role_t Role,long CtrCod);
 unsigned Usr_GetNumUsrsInCrssOfIns (Rol_Role_t Role,long InsCod);
 unsigned Usr_GetNumUsrsInCrssOfCty (Rol_Role_t Role,long CtyCod);