There is no single definitive test for PCOS. In North America, doctors usually diagnose PCOS based on the following criteria:

• a history of irregular periods (associated with a lack of ovulation)
• evidence of high levels of androgens or male-pattern hair growth
• an absence of other conditions which could explain the woman's symptoms

To diagnose PCOS, your doctor will do a physical exam, which may include a pelvic exam, and ask you questions about your medical history. Blood tests will be done to confirm the presence of high levels of male hormones, and rule out other potential causes of the symptoms. Your doctor may also want to test your blood sugar and cholesterol levels.

In addition, a vaginal ultrasound may be used to look for polycystic ovaries. Usually, an ultrasound diagnosis of PCOS is made if, in addition to other symptoms, there are at least eight to 10 cysts, which are less than 10 mm in diameter, on one or both ovaries. A polycystic ovary is often one and a half to three times the size of a healthy ovary. The ovaries of women with PCOS do not have cysts in them, but rather, follicles that have failed to produce mature eggs. This can result in the appearance of a "string of pearls" on the ultrasound. It is also possible to have PCOS but have ovaries that look normal. Doctors usually consider the finding of polycystic ovaries as a possible sign of PCOS, but do not rely on this as the sole criterion in diagnosing the condition.

Although most women with PCOS are overweight or obese, some women with PCOS are of a normal weight.