diff --git a/sort.1 b/sort.1
index 64613d8..1f375e9 100644
--- a/sort.1
+++ b/sort.1
@@ -3,7 +3,7 @@
 sort \- sort lines
 .SH SYNOPSIS
 .B sort
-.RB [ \-r ]
+.RB [ \-ru ]
 .RI [ file ...]
 .SH DESCRIPTION
 .B sort
@@ -13,3 +13,6 @@ given, sort reads from stdin.
 .TP
 .BI \-r
 reverses the sort.
+.TP
+.BI \-u
+prints repeated lines only once.
diff --git a/sort.c b/sort.c
index 130c549..c07702c 100644
--- a/sort.c
+++ b/sort.c
@@ -11,6 +11,7 @@ static int linecmp(const char **, const char **);
 static void getlines(FILE *, const char *);
 
 static bool rflag = false;
+static bool uflag = false;
 static char **lines = NULL;
 static long nlines = 0;
 
@@ -21,11 +22,14 @@ main(int argc, char *argv[])
 	long i;
 	FILE *fp;
 
-	while((c = getopt(argc, argv, "r")) != -1)
+	while((c = getopt(argc, argv, "ru")) != -1)
 		switch(c) {
 		case 'r':
 			rflag = true;
 			break;
+		case 'u':
+			uflag = true;
+			break;
 		default:
 			exit(EXIT_FAILURE);
 		}
@@ -39,12 +43,9 @@ main(int argc, char *argv[])
 	}
 	qsort(lines, nlines, sizeof *lines, (int (*)(const void *, const void *))linecmp);
 
-	for(i = 0; i < nlines; i++) {
-		fputs(lines[i], stdout);
-		free(lines[i]);
-	}
-	free(lines);
-
+	for(i = 0; i < nlines; i++)
+		if(!uflag || i == 0 || strcmp(lines[i], lines[i-1]) != 0)
+			fputs(lines[i], stdout);
 	return EXIT_SUCCESS;
 }