Cryptorchidism is the most common developmental disorder of endocrine organs in boys. Incidence depends on the age of the child--is the highest in the premature infants (30%), in term infants 2-5%, in adults 0.3%. Aetiology is still unclear and it is thought to be multifactorial including: dysgenesis of the testis, endocrine abnormalities and anatomical block on the way of the descent of the testis. In 90% of cases the pathology is unilateral. Abnormal localisation of the testis leads to the histomorphological changes which may be the causes of complications. The most dangerous are: infertility and neoplasms. The author presents also the diagnostic methods and therapeutic management in cryptorchidism.