A malignant Leydig cell tumor of the testis.

A 40-year-old man was referred to our hospital with gynecomastia and painless swelling of the right scrotum. Ultrasonography revealed a 15 x 10 mm mass with low echogenicity of the right testis. We performed right high orchiectomy. Histologically, Reinke's crystals and capsular invasion by tumor cells were found. Final diagnosis, the tumor was a malignant Leydig cell tumor of the testis.