Background: People in treatment for substance use disorder commonly have comorbid personality disorders, including antisocial personality disorder. Little is known about treatments that specifically address comorbid antisocial personality disorder. Methods: Self-rated help received for antisocial personality disorder was assessed during follow-ups at 3, 9 and 15 months post-randomization of a randomized trial of psychoeducation for people with comorbid substance use and antisocial personality disorder (n = 175). Results: Randomization to psychoeducation was associated with increased perceived help for antisocial personality disorder. Perceived help for antisocial personality disorder was in turn associated with more days abstinent and higher treatment satisfaction at the 3-month follow-up, and reduced risk of dropping out of treatment after the 3-month follow-up, and perceived help mediated the effects of random assignment on days abstinent at 3-month. follow-up. Conclusions: Brief psychoeducation for antisocial personality disorder increased patients' self-rated help for antisocial personality disorder in substance abuse treatment, and reporting having received help for antisocial personality disorder was in turn associated with better short-term outcomes, e.g., days abstinent, dropout from treatment and treatment satisfaction.