Cryptorchidism is defined as maldescensus testis. This means that one or both testicles are not located in the scrotum at six months of age, but abdominal, inguinal or ectopic. Ectopic testes can be localised suprafascially, perineally or crurally. Physiologically, descensus testis is finished about 35-40 days after birth in the dog and at the time of birth in the torn. Delayed descent is diagnosed when testis are located in the scrotum at a later point of time. Whereas cryptorchidism in the dog is undoubtedly multifactorial with breed-specific involvement of one or more genes (mono-/polygenic), epigenetic and environment-associated factors, heredity in the cat is still unclear although an increased incidence is reported in Persians, Ragdolls and European Shorthair. The diagnosis can be confirmed by palpation (in case of inguinal testes) or by ultrasound. GnRH and hCG stimulation tests can be used as an alternative in cases of suspected bilateral cryptorchidism with the aim of detecting a testosterone increase after a basal sample. Castration is the therapy of choice due to the increased risk for testicular tumours in the dog and the male sexual behaviour in the torn cat. Orchidopexy can be considered an alternative in the dog, bilateral vasectomy for permanent exclusion as a stud seems reasonable. The use of GnRH agonists or hCG in prepubertal cryptorchid males is discussed critically because it is still unclear whether they influence testicular descent since, in other species, testosterone is involved in the inguinoscrotal migration from the inguinal ring to the scrotum only.