diff --git a/RELNOTES b/RELNOTES
--- a/RELNOTES
+++ b/RELNOTES
@@ -10,6 +10,16 @@
 
 Changes to this file should not be MFCed.
 
+cccdbb57f741:
+	ps(1)'s '-U' option has been changed to select processes by their real
+	user IDs instead of their effective one, in accordance with POSIX and
+	the use case of wanting to list processes launched by some user, which
+	is expected to be more frequent than listing processes having the rights
+	of some user.  This only affects the selection of processes whose real
+	and effective user IDs differ.	After this change, ps(1)'s '-U' flag
+	behaves differently then in other BSDs but identically to that of
+	Linux's procps and illumos.
+
 935ffbe06f1d:
 	ps(1)'s default list of processes now comes from matching its effective
 	user ID instead of its real user ID with the effective user ID of all
diff --git a/bin/ps/ps.c b/bin/ps/ps.c
--- a/bin/ps/ps.c
+++ b/bin/ps/ps.c
@@ -349,20 +349,6 @@
 			 */
 			nselectors++;
 			break;
-#if 0
-		case 'R':
-			/*-
-			 * XXX - This un-standard option is still under
-			 *	debate.  This is what SUSv3 defines as
-			 *	the `-U' option, and while it would be
-			 *	nice to have, it could cause even more
-			 *	confusion to implement it as `-R'.
-			 */
-			add_list(&ruidlist, optarg);
-			xkeep_implied = 1;
-			nselectors++;
-			break;
-#endif
 		case 'r':
 			sortby = SORTCPU;
 			break;
@@ -394,21 +380,34 @@
 			nselectors++;
 			break;
 		case 'U':
+			add_list(&ruidlist, optarg);
+			xkeep_implied = 1;
+			nselectors++;
+			break;
+		case 'u':
+#if 0
 			/*
-			 * POSIX says that '-U' should match on real user IDs,
-			 * not effective ones as we are doing here, which is
-			 * normally the behavior of option '-u' according to the
-			 * standard.
+			 * POSIX's '-u' behavior.
+			 *
+			 * This has not been activated because:
+			 * 1. Option '-U' is a substitute for most users, and
+			 *    those that care seem more likely to want to match
+			 *    on the real user ID to display all processes
+			 *    launched by some users.
+			 * 2. '-u' has been a canned display on the BSDs for
+			 *    a very long time (POLA).
 			 */
 			add_list(&uidlist, optarg);
 			xkeep_implied = 1;
 			nselectors++;
 			break;
-		case 'u':
+#else
+			/* Historical BSD's '-u'. */
 			parsefmt(ufmt, &varlist, 0);
 			sortby = SORTCPU;
 			_fmt = 1;
 			break;
+#endif
 		case 'v':
 			parsefmt(vfmt, &varlist, 0);
 			sortby = SORTMEM;