The MR imaging appearance of a duodenal duplication cyst is reported. MR imaging confirmed the diagnosis suggested by ultrasound and CT scans. Fat-suppressed MR imaging before and after oral administration of the positive contrast agent Gd-DTPA was able to define tissue planes between the lesion and adjacent structures, such as the head of the pancreas, providing useful information for an accurate surgical approach. To our knowledge this is the first reported case of a duodenal duplication cyst in an adult demonstrated by MR imaging.