Hepatocellular carcinoma may share histologic features with a wide variety of epithelial tumors. To facilitate its pathologic diagnosis, clinical and pathologic material was reviewed from 62 patients with hepatocellular carcinoma and immunostaining was performed with polyclonal anti-carcinoembryonic antigen (pCEA), monoclonal anti-carcinoembryonic antigen (mCEA), anti-epithelial membrane antigen (EMA), and an antikeratin (KER AE1/AE3). Clinical information and follow-up were available for all patients from several sources. Cases with ambiguous clinical data or findings suggestive of metastatic carcinoma to the liver were excluded. In addition, the following tumors were immunostained and compared to hepatocellular carcinoma: 10 cholangiocarcinomas; 14 pancreatic adenocarcinomas; 4 gastric adenocarcinomas; 3 breast carcinomas; 5 renal carcinomas; 3 combined germ cell tumors of the testis; 3 adrenal cortical carcinomas; and 4 melanomas. The pCEA stained bile canaliculi in normal liver and in 39 of 62 (63%) hepatocellular carcinomas. This canalicular staining pattern of pCEA was unique to hepatocellular carcinoma. The mCEA (1 of 62, 1.6%) was almost always negative, and KER AE1/AE3 (9 of 59, 15.3%) was occasionally positive. The EMA stained 25 of 62 (40.3%). The adrenal cortical carcinomas and melanomas were negative for all antigens except rare pCEA and focal EMA staining in an adrenal tumor. Other carcinomas showed cytoplasmic pCEA (36 of 44, 81.8%), mCEA (40 of 46, 87.7%), EMA (41 of 43, 95.4%), and KER AE1/AE3 (42 of 44, 95.5%). Canalicular staining with pCEA is specific for hepatocellular carcinoma, while negativity with mCEA and KER AE1/AE3 is suggestive of hepatocellular differentiation.