diff --git a/regress/lib/libc/mbstowcs/Makefile b/regress/lib/libc/mbstowcs/Makefile
new file mode 100644
index 000000000000..663db4507539
--- /dev/null
+++ b/regress/lib/libc/mbstowcs/Makefile
@@ -0,0 +1,17 @@
+#	$NetBSD: Makefile,v 1.1 2004/02/26 23:29:46 itojun Exp $
+
+NOMAN=	# defined
+
+PROG=	mbtest
+
+regress: ${PROG}
+	LC_CTYPE=ja_JP.eucJP LANG= ./${PROG} < ${.CURDIR}/euc-jp.txt \
+		| diff ${.CURDIR}/euc-jp.output -
+	LC_CTYPE=ja_JP.SJIS LANG= ./${PROG} < ${.CURDIR}/sjis.txt \
+		| diff ${.CURDIR}/sjis.output -
+	LC_CTYPE=ja_JP.ISO2022-JP LANG= ./${PROG} < ${.CURDIR}/iso-2022-jp.txt \
+		| diff ${.CURDIR}/iso-2022-jp.output -
+	LC_CTYPE=en_US.UTF-8 LANG= ./${PROG} < ${.CURDIR}/utf8.txt \
+		| diff ${.CURDIR}/utf8.output -
+
+.include <bsd.prog.mk>
diff --git a/regress/lib/libc/mbstowcs/euc-jp.output b/regress/lib/libc/mbstowcs/euc-jp.output
new file mode 100644
index 000000000000..39db11be3979
--- /dev/null
+++ b/regress/lib/libc/mbstowcs/euc-jp.output
@@ -0,0 +1,7 @@
+setlocale = ja_JP.eucJP
+｣ﾅ｣ﾕ｣ﾃ､ﾇ､ｹ｡｣aaaa､｢､､､ｦ､ｨ､ｪ
+
+0xA3C5  0xA3D5  0xA3C3  0xA4C7  0xA4B9  0xA1A3  0x0061  0x0061  0x0061  0x0061  0xA4A2  0xA4A4  0xA4A6  0xA4A8  0xA4AA  0x000A  
+width:
+2 2 2 2 2 2 1 1 1 1 2 2 2 2 2 0 
+wcswidth=26
diff --git a/regress/lib/libc/mbstowcs/euc-jp.txt b/regress/lib/libc/mbstowcs/euc-jp.txt
new file mode 100644
index 000000000000..327d45ded877
--- /dev/null
+++ b/regress/lib/libc/mbstowcs/euc-jp.txt
@@ -0,0 +1 @@
+｣ﾅ｣ﾕ｣ﾃ､ﾇ､ｹ｡｣aaaa､｢､､､ｦ､ｨ､ｪ
diff --git a/regress/lib/libc/mbstowcs/iso-2022-jp.output b/regress/lib/libc/mbstowcs/iso-2022-jp.output
new file mode 100644
index 000000000000..a9e0e1b39f2d
--- /dev/null
+++ b/regress/lib/libc/mbstowcs/iso-2022-jp.output
@@ -0,0 +1,7 @@
+setlocale = ja_JP.ISO2022-JP
+$B#J#I#S$G$9!#(Baaaa$B$"$$$&$($*(B
+
+0x4200234A  0x42002349  0x42002353  0x42002447  0x42002439  0x42002123  0x0061  0x0061  0x0061  0x0061  0x42002422  0x42002424  0x42002426  0x42002428  0x4200242A  0x000A  
+width:
+2 2 2 2 2 2 1 1 1 1 2 2 2 2 2 0 
+wcswidth=26
diff --git a/regress/lib/libc/mbstowcs/iso-2022-jp.txt b/regress/lib/libc/mbstowcs/iso-2022-jp.txt
new file mode 100644
index 000000000000..7ac4fea338e1
--- /dev/null
+++ b/regress/lib/libc/mbstowcs/iso-2022-jp.txt
@@ -0,0 +1 @@
+$B#J#I#S$G$9!#(Baaaa$B$"$$$&$($*(B
diff --git a/regress/lib/libc/mbstowcs/mbtest.c b/regress/lib/libc/mbstowcs/mbtest.c
new file mode 100644
index 000000000000..7879f37a85b2
--- /dev/null
+++ b/regress/lib/libc/mbstowcs/mbtest.c
@@ -0,0 +1,71 @@
+/*	$NetBSD: mbtest.c,v 1.1 2004/02/26 23:29:46 itojun Exp $	*/
+/*-
+ * Copyright (c) 1999 Citrus Project,
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <locale.h>
+#include <wchar.h>
+
+int
+main(int ac, char **av)
+{
+	char	buf[256];
+	char	*str;
+	int	c;
+	wchar_t	wbuf[256];
+	wchar_t	*p;
+
+	printf("setlocale = %s\n", setlocale(LC_CTYPE, ""));
+
+	for (str = buf; 1; str++) {
+		c = getchar();
+		if (c == EOF || c == '\n')
+			break;
+		*str=c;
+	}
+	*str='\0';
+	strcat(buf, "\n");
+
+	mbstowcs(wbuf, buf, sizeof(buf) - 1);
+	wcstombs(buf, wbuf, sizeof(buf) - 1);
+	printf("%s\n", buf);
+
+	for (p = wbuf; *p; p++) {
+		printf("0x%04X  ", (unsigned)*p);
+	}
+	putchar('\n');
+
+	printf("width:\n", buf);
+		for (p=wbuf; *p; p++) {
+		printf("%d ", wcwidth(*p));
+	}
+	putchar('\n');
+
+	printf("wcswidth=%d\n", wcswidth(wbuf, sizeof(wbuf) - 1));
+
+	return 0;
+}
diff --git a/regress/lib/libc/mbstowcs/sjis.output b/regress/lib/libc/mbstowcs/sjis.output
new file mode 100644
index 000000000000..69e46f6046e4
--- /dev/null
+++ b/regress/lib/libc/mbstowcs/sjis.output
@@ -0,0 +1,7 @@
+setlocale = ja_JP.SJIS
+ＳＪＩＳです。aaaaあいうえお
+
+0x8272  0x8269  0x8268  0x8272  0x82C5  0x82B7  0x8142  0x0061  0x0061  0x0061  0x0061  0x82A0  0x82A2  0x82A4  0x82A6  0x82A8  0x000A  
+width:
+2 2 2 2 2 2 2 1 1 1 1 2 2 2 2 2 0 
+wcswidth=28
diff --git a/regress/lib/libc/mbstowcs/sjis.txt b/regress/lib/libc/mbstowcs/sjis.txt
new file mode 100644
index 000000000000..d7d7f8295a9f
--- /dev/null
+++ b/regress/lib/libc/mbstowcs/sjis.txt
@@ -0,0 +1 @@
+ＳＪＩＳです。aaaaあいうえお
diff --git a/regress/lib/libc/mbstowcs/utf2.txt b/regress/lib/libc/mbstowcs/utf2.txt
new file mode 100644
index 000000000000..503819785197
--- /dev/null
+++ b/regress/lib/libc/mbstowcs/utf2.txt
@@ -0,0 +1 @@
+[
][ﾂ�ﾟｿ][燿��ｿｿ][�逗��ｿｿｿ][������ｿｿｿｿ][�о����ｿｿｿｿｿ]
diff --git a/regress/lib/libc/mbstowcs/utf8.output b/regress/lib/libc/mbstowcs/utf8.output
new file mode 100644
index 000000000000..17ac5fd102a7
--- /dev/null
+++ b/regress/lib/libc/mbstowcs/utf8.output
@@ -0,0 +1,7 @@
+setlocale = en_US.UTF-8
+[
][ﾂ�ﾟｿ][燿��ｿｿ][�逗��ｿｿｿ][������ｿｿｿｿ][�о����ｿｿｿｿｿ]
+
+0x005B  0x0001  0x007F  0x005D  0x005B  0x0080  0x07FF  0x005D  0x005B  0x0800  0xFFFF  0x005D  0x005B  0x10000  0x1FFFFF  0x005D  0x005B  0x200000  0x3FFFFFF  0x005D  0x005B  0x4000000  0x7FFFFFFF  0x005D  0x000A  
+width:
+1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 0 
+wcswidth=12
diff --git a/regress/lib/libc/mbstowcs/utf8.txt b/regress/lib/libc/mbstowcs/utf8.txt
new file mode 100644
index 000000000000..503819785197
--- /dev/null
+++ b/regress/lib/libc/mbstowcs/utf8.txt
@@ -0,0 +1 @@
+[
][ﾂ�ﾟｿ][燿��ｿｿ][�逗��ｿｿｿ][������ｿｿｿｿ][�о����ｿｿｿｿｿ]