Forty-eight of the 50 living adult offspring of 16 bipolar patients were interviewed. Data was available on the 2 other offspring, who had previously suicided. One half of the offspring met criteria for psychiatric illness, the majority of which was either primary affective or other affective disorder. The mean age of onset of illness was middle to late adolescence, earlier than that generally reported elsewhere. Female offspring were 3 times as likely to be ill as male offspring, in spite of being equally represented in the sample. Reasons for this were examined.