Fusion of the testis and epididymis, histological findings of the undescended testis and location of the testis were studied in 90 undescended testes of eighty-one cryptorchid patients. Abnormal fusion of the testis and epididymis in the undescended testis were classified into four types : a) fusion of the testis and epididymis at the testicular cranial side. b) fusion of the testis and epididymis at the testicular caudal side. c) abnormal mesorchial fusion. d) complete separation. Thirty one undescended testes (34 percent) had abnormal fusion of testis and epididyms. The more cranial was the location of undescended testes, the more frequent was abnormal fusion of the testis and the epididymis. The testicular dysgenesis, which was expressed by tubular fertility index, was observed more frequently in the undescended testes of abnormal fusion and more cranially located testes. There results suggested that normal testicular morphogenesis is essential to normal descent of the testis and normal fusion of the testis and epididymis.
