We compared the social communication deficits of children with moderate to severe acquired brain injury or autism spectrum disorder, while accounting for the role of attention-deficit hyperactivity disorder (ADHD) symptoms. Parents of 20 children aged 6 to 10 years (10 acquired brain injury; 10 autism spectrum disorder) completed the Social Communication Questionnaire, and Conners 3 Parent Short. A multivariate analysis of covariance revealed significant differences between groups in Social Communication Questionnaire restricted repetitive behavior scores, but not reciprocal social interaction or social communication. Multiple linear regressions indicated diagnosis did not predict reciprocal social interaction or social communication scores and that Conners 3 Parent Short Form hyperactivity scores were the strongest predictor of Social Communication Questionnaire reciprocal social interaction scores after accounting for age and Intelligence Quotient. The lack of difference in social communication deficits between groups may help in understanding the pathophysiology underlying the behavioral consequences of acquired brain injury. The link between hyperactivity and reciprocal interaction suggests that targeting hyperactivity may improve social outcomes in children following acquired brain injury.