OBJECTIVE To determine whether paternity is decreased among men who were formerly unilaterally or bilaterally cryptorchid and to ascertain whether paternity is related to their age at orchidopexy. METHODS Men who underwent orchidopexy between 1955 and 1969 at the Children's Hospital of Pittsburgh (363) and a group of age-matched control men (336) were surveyed by questionnaire and their medical records reviewed. RESULTS Of the married men, significantly more of the unilateral cryptorchid (75%) and control (76%) groups had fathered children than had the bilateral cryptorchid group (P < 0.005). Furthermore, when the groups were compared during the period of regular intercourse with no contraception until conception of their first child, the bilateral group had relatively fewer conceptions during the first year and more after the first year. When the unilateral and bilateral groups were analysed separately, there was no relationship between either age at orchidopexy and paternity or between the age at orchidopexy and the duration of regular unprotected intercourse before conception. CONCLUSIONS Compared with a control group, paternity was compromised after bilateral, but not unilateral, cryptorchidism. Age at orchidopexy was not correlated with paternity.