Glans penis and foreskin lesions occurred in 16 patients (.+-.34%) in a group of 46 males with trichomoniasis and were predominantly of the erosive type. Trichomonal balano-posthitis has been associated with trichomonal urethritis in 7 patients, syphilis in 4 patients and genital warts in 4. The dominant complication was phimosis. Long foreskin should be considered a favorable condition in infection of glans penis and foreskin due to T. vaginalis. The dense predominantly lymphocytic infiltration in the upper dermis characterized the histology of the lesions. An inguinal lymph node biopsy specimen demonstrated the features of reactive hyperplasia, a cause of inguinal lymphadenopathy. The condition responded well to treatment with metronidazole during 9-10 days.