We examined co-occurrence of autism spectrum disorder (ASD) with (traits of) attention-deficit/hyperactivity (ADHD), obsessive-compulsive (OCD) and inhibition deficits in a community sample (n = 16,676) and tested whether having a sibling with ASD manifested in increased features of ADHD, OCD or inhibition deficits. Individuals with ASD had increased ADHD and OCD traits compared with individuals without ASD. Individuals with a sibling with ASD exhibited more ADHD traits than did individuals whose sibling did not have ASD. The "sibling effect" on manifestation of ADHD traits was observed in individuals with and without ASD. Having a sibling with ASD did not affect OCD traits. Inhibition was impaired in individuals with ASD who had a sibling with ASD only.