Ovarian cystic follicles are the sign of important causes of reproductive failure in numerous species. In this review, some morphological, endocrinological and clinical aspects of cystic follicles in women, cows, mares, sows and bitches are discussed. Follicular cysts are the consequence of the failure of a mature follicle to ovulate at the appointed time of ovulation in the estrous cycle. Although the etiology of follicular cysts remains unknown, this review examines the evidence about the role of endocrine signaling systems in the specific disease or syndrome in each of the species mentioned above. This review also describes, the changes in the pathways of endocrine mechanisms that would trigger disturbances in the intraovarian component underlying the aberrant persistence of follicular cysts. The knowledge of the morphological and endocrinological nature of cystic follicles in different species can provide relevant information to better understand specific diseases when it is integrally analyzed from the comparative medicine viewpoint.