Mycosis fungoides is a cutaneous T-cell lymphoma that can disseminate to multiple organs. We report a patient who presented with obstructive jaundice caused by isolated involvement of the extrahepatic biliary tree by mycosis fungoides. Initially, endoscopic examinations and biopsies of the biliary tree and liver failed to reveal a cause for the obstructive symptoms. Finally, surgical resection of the gallbladder and extrahepatic ducts was performed. Examination revealed a dense, mixed lymphocytic infiltrate with atypical cells within the mucosa. Gene rearrangement studies confirmed the presence of a monoclonal T-cell population. The pattern of the gene rearrangement in the biliary tree was identical to that found in a previous skin biopsy that showed mycosis fungoides. Although liver involvement by mycosis fungoides is not uncommon, disease isolated to the extrahepatic biliary tree has not previously been reported. This case should alert clinicians and pathologists to yet another cause of obstructive jaundice.