Leydig cell tumor [German anatomist Franz Leydig, 1821-1908] , a generally benign neoplasm of interstitial cells of a testis that may cause gynecomastia in adults and precocious sexual development if the lesion occurs before puberty. Less commonly it occurs in the ovary and causes androgenic symptoms. The tumor is usually a circumscribed lobulated palpable mass. Symptoms typically resolve after excision. Compare Sertoli-Leydig cell tumor.
