wikipedia has a wonderful description. I paste the beginning but please go to the page to get the full description
Polycystic Ovary Syndrome (abbreviated PCOS or PCO), also known clinically as Stein-Leventhal syndrome, is an endocrine disorder that affects approximately 10% of all women . It occurs amongst all races and nationalities, is the most common hormonal disorder among women of reproductive age, and is a leading cause of infertility. The principal features are weight problems, lack of regular ovulation and/or menstruation, and excessive amounts or effects of androgenic (masculinizing) hormones. The symptoms and severity of the syndrome vary greatly between women. While the causes are unknown, insulin resistance, diabetes and obesity are all strongly correlated with PCOS
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