Persistent discharge of milk or milk-like secretions from the udder, the appearance of which is visible in mares that are not pregnant or after weaning, is called galactorrhea. It is clinically manifested by mild to moderate amounts of mammary gland secretions andthe udder is slightly enlarged. The etiology of this condition is not sufficiently documented and there is little information on the incidence and frequency of individual episodes, the composition of secretions and the treatment of galactorrhea itself. The most accepted theory of galactorrhea in non-pregnant mares is due to elevated prolactin levels, secondary to Cushing's syndrome. However, in the absence of evidence of the existence of this syndrome, galactorrhea is diagnosed as idiopathic. The literature suggests the treatment of idiopathic galactorrhoea with the dopamine agonist called bromocriptine, otherwise used in the treatment of hyperprolactinaemia in human medicine, and in veterinary medicine the drug of choice for the treatment of equine Cushing's syndrome. In this diploma thesis, the case of a 17-year-old warmblood mare was presented, who showed symptoms of galactorrhea three times in the past two years and was not pregnant. At the udder's pressure, a whitish, milk-like secretion dripped from it without the admixture of rags, and the udder was untempered and painless to the touch. Hyperprolactinemia, secondarily caused by equine Cushing’s syndrome, was rejected as a diagnosis based on negative biochemical test results. The findings of milk cytology and bacteriological culture of udder secretions did not indicate potential mastitis or neoplasia. Based on the performed diagnostic procedures and the obtained results, and without other visible clinical disorders, the conclusion of the final diagnosis is idiopathic galactorrhea.