A rare case of male internal pseudohermaphroditism is described. The patient had normal external male sexual characteristics but unilateral cryptorchidism. Three of his four brothers had also cryptorchidism and were also involuntary infertile. One of them was later operated and a uterus found intra-peritoneally. The patient’s parents were cousins and the possible importance of an inheritable defect is discussed. The patient’s karyotype was normal.