Complete agenesis of the dorsal pancreas has rarely been described. Complete agenesis of the dorsal pancreas in a female who developed insulin-dependent diabetes mellitus at the age of 39 years is reported. The diagnosis of agenesis of the dorsal pancreas was suspected by abdominal ultrasound and confirmed by abdominal computed tomography (CT), magnetic resonance imaging, and endoscopic retrograde pancreatography. Her exocrine pancreatic function was essentially normal. Both of the patient's sons also had agenesis of the body and tail of the pancreas verified by abdominal CT but had no evidence of diabetes mellitus. This familial occurrence of agenesis of the dorsal pancreas suggests that hereditary mechanisms may play a role in the pathogenesis of this anomaly.