Many autistic young people exhibit co-occurring behavior difficulties, characterized by conduct problems and oppositional behavior. However, the causes of these co-occurring difficulties are not well understood. Impairments in theory of mind (ToM) are often reported in autistic individuals and have been linked to conduct problems in nonautistic individuals. Whether an association between ToM ability and conduct problems exists in autistic populations, whether this association is similar between individuals who are autistic versus nonautistic, and whether these associations are specific to conduct problems (as opposed to other domains of psychopathology) remains unclear. ToM ability was assessed using the Frith-Happé Triangles task in a pooled sample of autistic (N = 128; mean age 14.78 years) and nonautistic youth (N = 50; mean age 15.48 years), along with parent-rated psychiatric symptoms of conduct problems, hyperactivity/inattention and emotional problems. Analyses tested ToM ability between autistic versus nonautistic participants, and compared associations between ToM performance and conduct problems between the two groups. Where no significant group differences in associations were found, the pooled association between ToM and conduct problems was estimated in the combined sample. Results showed no evidence of moderation in associations by diagnostic status, and an association between poorer ToM ability and higher levels of conduct problems, hyperactivity/inattention and emotional problems across the total sample. However, these associations became nonsignificant when adjusting for verbal IQ. Results provide support for theoretical models of co-occurring psychopathology in autistic populations, and suggest targets for intervention for conduct problems in autistic youth. LAY SUMMARY: Many young people with autism spectrum disorder show co-occurring behavior problems, but the causes of these are not well understood. This paper found an association between difficulties recognizing what others think and intend (so-called “theory of mind”) in a simple animated task, and emotional and behavioral problems in autistic and nonautistic young people. However, a substantial part of this association was explained by individual differences in verbal ability. These findings may have implications for intervention efforts to improve young people’s mental health.© 2020 The Authors. Autism Research published by International Society for Autism Research and Wiley Periodicals LLC.