To evaluate the heritability of a personality trait, "having temper outbursts," and of associated diagnoses, we obtained histories of first degree relatives on two groups: (1) patients with temper outbursts (N = 33), and (2) diverse psychiatric patients without temper outbursts (N = 12). Family interviews were conducted blind to patient (temper or not) status, using a modified version of the Family History RDC. Though Ns are relatively small, and results therefore require confirmation, the data indicate familial transmission of temper problems; an average of 18.2% of Group 1 relatives had temper problems, compared to 4.3% for Group 2. The trait of having temper outbursts was more strongly transmitted than were specific diagnoses (e.g. Intermittent Explosive Disorder, Antisocial Personality Disorder or Residual Attention Deficit Disorder) associated with temper outbursts. Patients with neurological conditions apparently related to their temper outbursts were less likely to have positive family histories.