We have investigated the use of inhibin and cytokeratin-7 (CK-7) in distinguishing endometrioid ovarian carcinomas (both typical and sex cord-like) form granulosa cell and Sertoli cell-containing ovarian tumors. Immunohistochemical staining with inhibin, CK-7, and epithelial membrane antigen (EMA) was performed on 6 endometrioid carcinomas simulating sex cord-stromal tumors, 5 typical endometrioid carcinomas, 14 adult granulosa cell tumors (AGCTs), 3 Sertoli-Leydig cell tumors (SCLTs), and 1 sex cord tumor with annular tubules (SCTAT). All AGCTs and SLCTs as well as the SCTAT were inhibin-positive. In contrast, all of the endometrioid carcinomas (both typical and those mimicking sex cord-stromal tumors) were inhibin-negative. CK-7 expression was not observed in the granulosa cell tumors and it was noted only in retiform areas in SLCTs. All 5 typical endometrioid carcinomas and 5 of the 6 sex cord-like endometrioid carcinomas were CK-7 positive. EMA was positive in all carcinomas but negative in the SCTAT, AGCTs, and SLCTs. Inhibin can distinguish between sex cord-stromal tumors (whether granulosa or Sertoli-Leydig type) and endometrioid carcinomas. CK-7 is also helpful in differentiating between AGCTs and most endometrioid carcinomas, and may also aid in separating SLCTs from sertoliform carcinomas. The addition of inhibin to an antibody panel is important because it provides a positively-staining marker for sex cord-derived cells.