Paternity has been studied among married men who were formerly cryptorchid. Forty-one of 52 formerly unilateral cryptorchid men were married, 10 of 11 bilaterally cryptorchid and 36 of 42 control men. Thirty-two of the 41 of the unilateral group (78%) had fathered children, 6 of 10 in the bilateral group (60%) and 24 of 36 controls (67%). These limited data from the initial phase of this study of paternity after cryptorchidism do not show any correlation between paternity or time of unprotected intercourse to conception and age of surgery or pretreatment testicular size or location. However, these data suggest that paternity is not decreased after unilateral cryptorchidism.