Cystic endometriosis of the epididymis.

Endometriosis of the male genitourinary tract is an exceedingly rare entity, with only 6 cases reported to date involving the bladder, prostate, lower abdominal wall, and paratesticular region. We present what we believe to be the first case of cystic endometriosis of the epididymis in a 27-year-old man with scrotal pain, describe its pathologic and immunohistochemical features, and discuss its pathogenesis.