Polycystic Ovary Syndrome(PCOS) was originally reported by Stein and Leventhal in 1935, as an syndrome with bilateral polycystic ovaries, menstrual abnormality, hirsutism and obesity etc. After this report the diagnosis of "Polycystic Ovary" was abused for the patient only with polycystic change of ovaries, so that, the concept or definition of PCOS has became unclear and controversial. In this review, a classification of PCOS according to the presence of hyperandrogenemia and/or hirsutism will be shown to reconstruct the concept or definition of PCOS. And usefulness of this classification will be revealed by showing endocrinological and morphological aspect of each class. Furthermore, new therapeutic approaches for PCOS with pure FSH injection in combination with GnRH analog against the onset of OHSS, or drillings of antral follicles with CO2 or KTP laser will be also shown in this review.