A routine prenatal sonographic examination at 37 weeks' menstrual age revealed a large sonolucent lesion with peristaltic movement in the abdomen of a fetus. After birth, the female infant showed progressive abdominal distention, and radiography showed a bubble-like dilatation of the small intestine. Exploratory laparotomy revealed ileal atresia with nearby partial torsion of the dilated small bowel. The incomplete torsion may have functioned as a check valve, inducing segmental dilatation of the ileum without proximal dilatation.