A 3-month-old boy is brought to the physician because his parents cannot find one of his testicles. Physical examination confirms the parents' observation. Which of the following is the most likely diagnosis?

Cryptorchidism, clinically known as undescended testis, is a congenital abnormality in which one or both testes are not found in their normal position in the scrotum. It is the most common urologic condition requiring surgical treatment in infants. In 5% of male infants born at term and 30% of those born prematurely, the testes are not located in the scrotum or are easily retracted. In the large majority of these infants, the testis will descend into the scrotum during the first year of life. The descent of the testis may be arrested at any point from the abdominal cavity to the upper scrotum. According to their location, the cryptorchid testes can be classified as abdominal, inguinal, or upper scrotal. Anorchia (choice A) refers to congenital absence of testes. Macroorchidism (choice D) is a pathologic finding in adult patients with fragile X syndrome.Diagnosis: Cryptorchidism