No randomized clinical trials have evaluated the efficacy of psychotherapy for intermittent explosive disorder (IED). In the present study, the authors tested the efficacy of 12-week group and individual cognitive-behavioral therapies (adapted from J. L. Deffenbacher & M. McKay, 2000) by comparing them with a wait-list control in a randomized clinical trial among adults with IED (N = 45). Aggression, anger, and associated symptoms were assessed at baseline, midtreatment, posttreatment, and 3-month follow-up. Group and individual cognitive-behavioral therapy tended not to differ, with each reducing aggression, anger, hostile thinking, and depressive symptoms, while improving anger control relative to wait-list participants. Posttreatment effect sizes were large. These effects were maintained at 3-month follow-up. Findings provide initial support for the use of multicomponent cognitive-behavioral therapy in the treatment of IED.