The objective of this study was to determine whether the familial aggregation of suicidal behaviour is explained by the familial aggregation of personality disorder and aggression. The relatives of 62 clinically referred adolescent suicide attempters were compared with 70 never-suicidal psychiatric controls. The first-degree relatives of the suicide attempters had a higher rate of suicide attempts/completion than those of the psychiatric controls. This rate remained significantly higher after controlling for Axis I and II differences in the probands and the relatives, but familial personality disorder was significantly associated with suicidal risk in probands. Among the adolescent attempters, high scores on a measure of assaultiveness were associated with significantly higher familial rates of suicide attempts/completion. Our results support the hypothesis that suicidal behaviour may be transmitted as a trait independent of Axis I and II psychopathology but that, in addition, personality disorder has a role in the transmission of suicidal behaviour. An interrelationship between proband assaultiveness and the familial aggregation of suicidality was noted.