OBJECTIVES: To examine the prevalence of language problems in children with attention-deficit/hyperactivity disorder (ADHD) versus non-ADHD controls, and the impact of language problems on the social and academic functioning of children with ADHD. METHODS: Children (6 to 8 years) with ADHD (n = 179) and controls (n = 212) were recruited through 43 Melbourne schools. ADHD was assessed by using the Conners 3 ADHD Index and the Diagnostic Interview Schedule for Children IV. Oral language was assessed by using the Clinical Evaluation of Language Fundamentals, fourth edition, screener. Academic functioning was measured via direct assessment (Wide Range Achievement Test 4) and teacher report (Social Skills Improvement System). Social functioning was measured via parent and teacher report (Strengths and Difficulties Questionnaire; Social Skills Improvement System). Logistic and linear regression models were adjusted for sociodemographic factors and child comorbidities. RESULTS: Children with ADHD had a higher prevalence of language problems than controls after adjustment for sociodemographic factors and comorbidities (odds ratio, 2.8; 95% confidence interval [CI], 1.5 to 5.1). Compared with children with ADHD alone, those with language problems had poorer word reading (mean difference [MD], -11.6; 95% CI, -16.4 to -6.9; effect size, -0.7), math computation (MD, -11.4; 95% CI, -15.0 to -7.7; effect size, -0.8), and academic competence (MD, -10.1; 95% CI, -14.0 to -6.1; effect size, -0.7). Language problems were not associated with poorer social functioning. CONCLUSIONS: Children with ADHD had a higher prevalence of language problems than controls, and language problems in children with ADHD contributed to markedly poorer academic functioning.