A family study of psychiatric disorders in 2,003 first-degree relatives of 335 probands found increased rates of bipolar I disorder and major depression (MD) in the relatives of probands with bipolar disorder and increased rates of MD in the relatives of probands with MD. There was a similarity in rates of affective disorders in the relatives of ambulatory and of hospitalized depressed probands (suggesting that ambulatory depressed patients may be as suitable as hospitalized ones for biological studies) and a comparability of rates of illness in relatives between centers for most disorders when comparable diagnostic criteria and procedures were used.