Doctors don't know exactly why you get it, but some researchers think high levels of insulin are at the root of the illness. If you're overweight, your chances of developing it are greater.
Your genes play a role, too. If your mother or sister has PCOS, you're more likely to have it. Most women are diagnosed in their 20s or 30s. But even girls as young as 11, who haven't gotten their period yet, can have it.