Objective: A brief cognitive behavioral therapy (CBT) group intervention was designed to treat comorbid anxiety, depression, and low self-esteem and self-efficacy in adults with ADHD. It was hypothesised that participants would gain knowledge about ADHD, experience a reduction in comorbid symptoms, and benefit from the supportive aspect of group treatment. Method: Participants in the study formed a CBT treatment group that attended six workshops and a waiting list control group. The intervention was evaluated with measures assessing knowledge about ADHD, psychological symptoms, and support received. The groups were compared using repeated measures ANOVAs. Results: The CBT group had significantly greater improvement on measures of knowledge about ADHD, self-efficacy, and self-esteem than the control group. Participants' evaluations of the sessions suggested that sharing personal experiences with other adults with ADHD was an important aspect of the intervention. Conclusion: Brief CBT group treatments may be an acceptable and cost-effective intervention for adults with ADHD. (Contains 4 tables.)