The individual features of the Stein-Leventhal syndrome has been submitted to a step-by-step review by the author. After a critical study of its clinical manifestations, the author insisted on the variously hypothetized pathways of biosynthesis of ovarian steroids, commenting each one of them and drawing diagrams of special clarity. The alterations that can possibly occur in Stein-Leventhal syndrome: aromatization deficiency, partial enzymatic inhibition due to 3 beta ol dehydrogenase deficiency, have been investigated. To follow, the author discussed: the mechanism of adrenocortical interference, the part played by the pituitary gland and hypothalamus. In the author's opinion, four etiological types of the "micropolycystic ovarian syndrome" can be distinguished, according as the hypothalamic origin is a primary one or secondary to hereditary hypercorticism, and according as the biosynthesis inhibition takes place at the aromatization level or at the levels at which 3 beta ol dehydrogenase activity exerts itself. Interesting therapeutical and prognostic conclusions can be drawn from these suggestions.