The 'double bubble' sign in prenatal diagnosis is most often associated with duodenal atresia. However, other causes of upper intestinal obstruction and cystic abdominal masses need to be considered. One possible diagnosis that can mimic the 'double bubble' sign of duodenal atresia is duodenal duplication, but little information is available to guide sonologists in the prenatal diagnosis of this rare congenital anomaly. In this case report we describe the successful prenatal diagnosis of duodenal duplication, by relying on the early gestational age of presentation, the lack of polyhydramnios, the failure to consistently demonstrate a 'double bubble' on transverse images, and the presence of a normal distal bowel pattern.