BACKGROUND: Cryptorchidism is a congenital anomaly in which one (unilateral cryptorchidism) or both (bilateral cryptorchidism) testes fail to descend into the scrotum.                  OBJECTIVE: The aim of this study was to describe the anatomical and histological structure of the inguinal testis in the adult donkey. METHODS: In this study, after examination of the 59 donkeys, three of them with unilateral cryptorchidism in inguinal region were identified. These animals were euthanized, and their testicles were removed and evaluated biometrically. Then, the samples were fixated in 10% formalin solution and after sectioning, were stained with Hematoxylin-eosin and PAS, and examined under a light microscope. RESULTS: The results showed that the inguinal testes were stiff, epididymis was not determined and their size and weight were less than scrotal testes. The difference between the weight of cryptorchid and healthy testicles was statistically significant (p<0.05). Seminiferous tubules had lost their natural shape and inner cavity tubes did not have germ cells, and only a limited number of Sertoli cells could be seen. Remaining seminiferous tubules were only visible in the mediastinum. The cortical and subcapsular regions were without tubes and were occupied by loose connective tissues. CONCLUSIONS: Results indicated that the inguinal testes in adult donkeys lost their natural structure and more connective tissues and blood vessels are substituted.