Background Understanding motives for offending is important for the development and delivery of effective interventions. Aims To explore associations between variables with motivational implications and the offence committed in the past year rated by people with antisocial personality disorder and substance use disorder as putting them and their status at most risk. Methods Participants were 127 outpatients from a sample recruited for a pragmatic randomised controlled trial of an intervention for adults attending substance abuse treatment clinics in 13 municipalities in Denmark. Motives for offending were assessed on one occasion, using the Offending Motivation Questionnaire, aggression was assessed using the Buss–Perry Aggression Questionnaire and substance‐related problems, including mental state difficulties, were assessed using the Substance Use Risk Profile. Results Attributing offending to provocation, excitement or financial gain differed substantially by type of offence, whereas attribution of offending to compliance did not. Personality scale scores were associated with attributing offences to provocation, excitement or compliance but not with financial gain. Conclusions Motives for offending among substance users with antisocial personality disorder must be understood both in light of the type of offence and personality traits. Offending behaviour prevention strategies that draw on these distinctions, run in parallel to treatment for substance use, could improve reduction in recidivism. Copyright © 2017 John Wiley & Sons, Ltd.