There is a general consensus among surgeons and paediatricians that cryptorchidism should be detected and treated by the age of 5 years, if not earlier. In reality, incomplete descent is often detected well beyond the age of 5. The effectiveness of local screening was assessed by reviewing the screening history and subsequent management of boys treated for undescended testes between 1983 and 1986. The detection rates for undescended testes in the boys under 5 years were low both for doctors and health visitors. In contrast, the school entry medical examination for 5 and 6 year olds had a higher screening yield. Over 40% of cases came to light as a result of parents recognising the condition and seeking medical opinion. Late detection had also occurred in some boys who had had previous genital surgery or examination. Methods to improve early detection and ways of monitoring proposed changes are discussed.