Retroperitoneal benign cystic teratoma is relatively rare in adults. We report a case of traumatic rupture of primary retroperitoneal teratoma into peritoneum that produced chemical peritonitis. It was demonstrated by computed tomography, which showed fat-fluid levels in the peritoneum. We suggest that the demonstration of fat-fluid levels in the peritoneum could be a reliable sign of intraperitoneal rupture of abdominal teratoma and subsequent chemical peritonitis.