Undescended testis is a common finding in boys, and the majority of cases have no discernible aetiology. There are unexplained geographical differences and temporal trends in its prevalence. Cryptorchidism, especially bilateral, is associated with impaired spermatogenesis and endocrine function and increases the risk of testicular cancer. There is an urgent need to identify factors that adversely affect testicular development and optimize treatment. Conclusion: Cryptorchidism may reflect a primary testicular maldevelopment with long-term consequences.