Therapeutic alliance is widely considered one of the factors most associated with treatment success in psychotherapy across a variety of outcomes. However, these effects may differ based on treatment approach or who is rating alliance (client, therapist, or third-party observer). Notably, research on this relationship among individuals with primary aggression problems is limited, with no study to date investigating therapeutic alliance in psychotherapy among individuals with intermittent explosive disorder (IED), the only psychiatric disorder for which affective aggression is pathognomonic. The current study sought to fill this gap by exploring the role of therapeutic alliance on a range of outcomes among 51 adults with IED who participated in a randomized clinical trial comparing cognitive-behavioral and supportive psychotherapy. Therapeutic alliance was assessed by clients, therapists, and an observer at week four of treatment, and outcomes included time in treatment, anger, aggression, emotion dysregulation, and IED remission status. Results showed that alliance was positively associated with reduced anger and aggression at post-treatment. Although alliance was more highly rated in the cognitive-behavioral condition, the alliance-outcome relationship did not differ based on treatment condition. There were no differences found between raters of alliance. These findings support the importance of developing and maintaining a strong relationship in psychotherapy with individuals diagnosed with IED. / Psychology