The CT and ultrasound features of retained sponges (gossypibomas) are described in six patients. They are well-circumscribed cystic masses without surrounding edema. The retained sponges or towels were correctly identified in only three cases. In the other three cases retained sponges were organized and lost their original configuration. Gas was seen in one case and calcification in two cases. Gossypibomas should be included in the differential diagnosis in all patients with a well-circumscribed cystic mass in the abdomen and with a history of previous laparotomy.