Undescended testis (UDT) is a very frequent clinical finding in boys. Despite its relatively high frequency, a uniform classification suitable for clinical setting is not available for the disorder. The purpose of this study is to investigate the anatomical localizations of non-palpable testes and some potential aetiologic factors. We analysed the data for 133 patients with UDT. Physical examination and surgical outcomes of the patients were compared in terms of testicular localizations. Birth weight of the patients, gestational ages, presence of additional congenital anomalies, whether they were breastfed in infancy, age of the first diagnosis, maternal age during pregnancy, history of maternal diabetes and presence of Rh incompatibility. Using the described classification, the 101 right and 85 left impalpable testes were classified as follows: 15·8% Type I, 34·6% Type II, 17·3% Type III, 8·3% Type IV, 24·1% normal testes on the right side when manually examined. Left impalpable testes were classified as follows when manually examined as follows: 13·5% Type I, 26·3% Type II, 9·0% Type III, 15·0% Type IV and 36·1% normal testes. When we compared these results with surgical results, we found a statistically significant difference. Being familiar with anatomic localizations of undescended testes is of (vital) importance in terms of surgical approach and for possible postoperative complications. Although manual examination is an indispensable part of diagnosis, it may be insufficient to determine its localization, and thus further tests may be required. Further studies are required to investigate the aetiologic factors for UDT.