We examined expression patterns of the stem cell marker, undifferentiated embryonic cell transcription factor 1 (UTF1) in the testicular biopsy sample, and demonstrated that the UTF1-positive Ad spermatogonia / negative Ad spermatogonia ratio was lower in this patient than in boys his age with descended and inguinal undescended testes, indicating that spermatogonial stem cell activity may decrease remarkably in this boy.