This is the first report of inhibin-alpha expression in granular cell tumors. A Medline search of the literature revealed no case reports of granular cell tumors in any location of the body being tested for inhibin-alpha immunohistochemically, by enzyme-linked immunosorbent assay, by radioimmunoassay, or by immunoprecipitation. Seventeen cases of previously diagnosed granular cell tumors of the gallbladder and extrahepatic bile ducts with hematoxylin and eosin-stained sections, and S-100 protein immunostain were retrieved from the archives of the Armed Forces Institute of Pathology. All cases were reviewed for diagnostic accuracy and then immunostained for inhibin-alpha (with endogenous biotin blocking). All 17 (100%) cases were diffusely positive for inhibin-alpha immunostain. Previous studies of inhibin-alpha-positive lesions reported in the literature include sex cord stromal tumors (granulosa cell tumors, luteinized thecomas, Leydig cell tumors), placental and gestational trophoblastic lesions, and adrenal cortical tumors. This study adds the granular cell tumor to the list of inhibin-positive lesions and should prove helpful in differential diagnosis of these lesions.