Reports of co-morbid symptoms of ADHD in children with ASD have increased. This research sought to identify ADHD-related behaviours in a sample of children with ASD, and their relationship with the ASD triad of impairments and related cognitive impairments. Children with ASD (n = 55) completed a comprehensive cognitive assessment whilst a semi-structured parental interview (3Di) provided information on ASD and ADHD symptoms. Co-morbid presentation of ADHD traits in these participants was associated with reports of more ASD related behaviours. Inhibitory control performance was directly related only to the ADHD symptom of impulsive behaviour. In contrast, while there was a relationship between social difficulties associated with ASD and theory of mind ability, there was no such relationship with behaviours relating to ADHD.