An epidemiological study on undescended testis.

We present an epidemiological study of undescended testes. Of the cases of undescended testes two-thirds are bilateral. Undescended testes occur more often in the sons of less educated parents and mothers with lower qualified jobs. Our study led to 3 important etiological conclusions: 1) cases of undescended testes at birth and true undescended testes cases may represent somewhat different nosological entities, 2) unilateral and bilateral cases do not show any significant difference in epidemiological parameters and 3) the pituitary and chorionic gonadotrophins may have an important role in the occurrence of true undescended testes, as suggested by the season of birth.