We experienced a case of pancreaticobiliary maljunction in monozygotic twins. While one of the twins suffered from gallbladder cancer with poor prognosis, the other was not associated with biliary malignancy. Ultrasonography, endoscopic ultrasonography, and magnetic resonance cholangiopancreatography are effective in diagnosis of this disorder before occurrence of biliary cancers. This case is not only of academic interest for familial occurrence, but also of clinical interest in the early detection of pancreaticobiliary maljunction.