The diagnosis of polycystic ovary syndrome (PCOS) is primarily achieved through clinical history and physical findings. The principle features are hirsutism or biochemical evidence of excess androgen production and irregular menstrual bleeding caused by the chronic anovulation. Associated findings include insulin resistance with compensatory hyperinsulinemia and obesity. Ultrasound imaging of the ovary has facilitated the diagnosis. It is important to exclude conditions that may mimic PCOS, such as hyperthecosis, congenital adrenal hyperplasia, 21-hydroxylase deficiency, Cushing's syndrome, and androgen-producing neoplasms. These disorders are usually revealed by appropriate laboratory assessment. Screening tests include measurement of serum total testosterone, DHEA sulfate, and 17-hydroxyprogesterone. In addition, in the obese individual, determinations of glucose and insulin levels, as well as a lipid profile, are highly recommended.