OBJECTIVES: To examine the functional status (mental health, academic performance, peer problems) of a community-based sample of children who have attention-deficit/hyperactivity disorder (ADHD) and non-ADHD controls, and to investigate gender and subtype differences. METHODS: Children aged 6 to 8 years were recruited through 43 Melbourne schools, using a 2-stage screening (parent and teacher Conners 3 ADHD index) and case confirmation (Diagnostic Interview Schedule for Children, Version IV; [DISC-IV]) procedure. Outcome measures were mental health disorders (DISC-IV), academic performance (Wide Range Achievement Test 4), and peer problems (Strength and Difficulties Questionnaire). Unadjusted and adjusted linear and logistic regression were used to compare ADHD and non-ADHD controls. RESULTS: A total of 179 children who have ADHD and 212 non-ADHD controls were recruited. Compared with controls, children who had ADHD had higher odds of externalizing (odds ratio [OR], 11.0; 95% confidence interval [CI], 5.6-21.6; P < .001) and internalizing (OR, 2.9; 95% CI, 1.2-7.2; P = .02) disorders; poorer reading (effect size, -0.66) and mathematics (effect size, -0.69) performance; and more peer problems (P < .001). Boys and girls who had ADHD were equally impaired. Only 17% of children in our ADHD group had been previously diagnosed. Previous diagnosis was higher in the Combined group and for boys. CONCLUSIONS: In their second year of school, children who had ADHD performed worse than controls across all functional domains, yet only a minority had been formally diagnosed with ADHD. Findings highlight the need for earlier diagnosis and intervention.