While the exact cause of PCOS is unknown, it runs in families, so the tendency to develop the syndrome may be inherited. The interaction of hyperinsulinemia and hyperandrogenism is believed to play a role in chronic anovulation in susceptible women.

The numbers and types of PCOS symptoms that appear vary among women. These include:

• Hirsutism. Related to hyperandrogenism, this occurs in 70% of women.
• Obesity. Approximately 40–70% of persons with PCOS are overweight.
• Anovulation and menstrual disturbances. Anovulation appears as amenorrhea in 50% of women, and as heavy uterine bleeding in 30% of women. However, 20% of women with PCOS have normal menstruation.
• Male-pattern hair loss. Some women with PCOS develop bald spots.
• Infertility. Achieving pregnancy is difficult for many women with PCOS.
• Polycystic ovaries. Most, but not all, women with PCOS have multiple cysts on their ovaries.
• Skin discoloration. Some women with PCOS have dark patches on their skin.
• Abnormal blood chemistry. Women with PCOS have high levels of low-density lipoprotein (LDL or "bad") cholesterol and triglycerides, and low levels of high-density lipoprotein (HDL or "good") cholesterol.
• Hyperinsulinemia. Some women with PCOS have high blood insulin levels, particularly if they are overweight.