Malignant lymphoma rarely presents with jaundice. We describe a patient who had a unique etiology for painless jaundice, dilated ducts, and a normal ampulla of Vater. A Whipple's procedure was performed for the suspicion of pancreatic cancer, and initial pathological review detected only mild focal chronic pancreatitis. Seven months later, the patient developed ascites, retroperitoneal mass, and splenomegaly caused by a T-cell lymphoma. Reevaluation of the Whipple's specimen revealed previously unrecognized microscopic infiltration and fibrosis of the sphincter of Oddi by atypical T-lymphocytes. Obstructive jaundice caused by a clinically undetectable primary duodenal T-cell lymphoma has not been previously reported and is contrasted with other causes of jaundice associated with malignant lymphoma and ampullary lesions.