MONDO_0003124 (testicular Leydig cell tumor) is a sex cord-stromal tumor that arises from the testis and is characterized by the presence of cells that resemble the successive stages of development of Leydig cells. It usually presents as a painless testicular mass. Gynecomastia is present in approximately thirty percent of the cases. Libido may be decreased. In children, precocious puberty may be present. A minority of cases exhibit malignant characteristics. Also known as: Leydig cell neoplasm of testis, Leydig cell neoplasm of the testis, Leydig cell tumor of testis, Leydig cell tumour of testis, testicular Leydig cell neoplasm, testis Leydig cell tumor, testis Leydig cell tumour.