Family history was examined to determine whether suicide in index patients is associated with suicidal behaviour or mental disorder in their first-degree relatives. Twenty-seven suicides occurred within 5 1/2 years among 955 affectively disordered probands. Among 5042 proband relatives aged 18 years and older, 44 had committed suicide prior to proband entry to the study; however, only one was the relative of a proband suicide. Only two of the relatives who committed suicide were themselves related. As to attempted suicide of relatives, neither the number of attempts nor the severity of attempt was predictive of suicide in probands. Comparison of diagnosis between groups of relatives showed more drug abuse among relatives of proband suicides; this appears to be related to drug abuse among the proband suicides themselves. In contrast to the clustering of suicides within biological families found in other research, these data do not support the use of family history as a clinically useful indicator of suicidal potential in affectively disordered probands.