Earlier, the cause of infertility in undescended testis (UT) had been widely accepted as a consequence of the higher temperature of the inguinal/abdominal region. Observations made in the past two decades, however, gave new evidences. The most important of these is that UT is often associated with the fusional anomalies (FA) of the testis and epididymis. FA is the consequence of pathological intrauterine hormonal processes and many authors believe FA to be the primary cause for infertility in UT. Since 80% of UT cases are of endocrine origin, it would be suspected that the very same factors are responsible for both UT and FA. FA and other anomalies of the epididymis often occur in testicular torsion (TT) as well. It is remarkable that infertility could follow the unilateral forms of UT and TT despite the presence of a "healthy" contralateral gonad. In both entities contralateral FA (probably associated with testicular dysgenesis) is suspected. These observations could influence the primary surgical treatment of patients with UT and TT, as well as the mode of further management of these cases.