How common is manic depression in teens?

Of the people who suffer from depressive disorders, about 1-2% have manic depression. It is not terribly common, especially in teenagers, but it is real and very disruptive of the sufferer’s life. Most people who have bipolar disorder first start to show symptoms in their early twenties, but this could be because it had been previously misdiagnosed or confused for something else. Of the adults who eventually are diagnosed with bipolar, about half had their first episode before age 17, and about 20% had their first episode between the ages of 10 and 14.