Hyperadrenocorticism or Cushing's disease is a disease that is caused by prolonged exposure of the body to excessive amounts of cortisol secretion. Therefore, a lack of the normal response exists within the mechanism hypothalamic-pituitary-adrenal gland, as well as a lack of the normal rhythm of cortisol secretion. As a disease, hyperadrenocorticism comes in two basic forms; caused by a pituitary disease or by adrenal tumors. Most dogs with hyperadrenocorticism slowly develop clinical symptoms and the owner can notice them only in the more severe form when they develop several clinical symptoms. Polydipsia, polyuria and polyphagia are the most typical symptoms. The disease occurs in dogs older than 6 years. There is a breed predisposition: Poodles, Dachshunds, Beagles, German shepherds, Labrador retrievers and Terriers were most commonly represented among the huge number of breeds. When the basic methods of clinical studies suspect hyperadrenocorticism, the endocrine testing should be completed. There are several different screening tests, but they all give a false positive result, because tests can be positive on some other diseases. Medical therapy may be selected depending on the type of hyperadrenocorticism.