Abstract: Although the aetiology of polycystic ovary syndrome（PCOS） is unknown and the search for causative genes is elusive，androgen excess is generally thought of an important triggers of PCOS.We known that excess androgens is the root cause of PCOS starting from the female fetus，producing the characteristic signs and symptoms which are then exacerbated by the excess ovarian androgen production from multiple small follicle，anovulation and insulin resistance in the reproductive life-span，thus setting up a vicious perpetual circle of excess androgen.The paper is biased in support of the hypothesis that androgen excess is the“root of all evil”in PCOS.

Key words: Androgens, Polycystic ovary syndrome, Ovary, Anovulation, Insulin resistance