A total of 1386 operations for undescended testis was made in 1250 boys. In 774 of them an apparently intact testis and epididymis were found. In 612, such epididymal developmental abnormalities were detected which exclude or do not make possible the passage of sperms from these organs to the deferent duct. It is believed to be plausible that the large number of cases with infertility is due, also in individuals with a unilateral cryptorchidism, to the abnormal fusion of the epididymis in both testes.