Using a sample of 268 patients and 137 community-based children with DSM-IV ADHD, and 268 school controls, aged 6–15, this study aimed to compare the emotional/behavioral problems and functional impairment between clinic- and community-based children with ADHD. Children’s ADHD-related symptoms, a wide range of emotional/behavioral problems, and functional impairments were assessed by the psychiatric interviews and self-, parent- and teacher-reported questionnaires. Both ADHD groups scored higher in parent- and teacher-reported ADHD-related symptoms, wide-ranging emotional/behavioral problems, and impairments in the school, peer, family, and leisure time domains than school controls. However, clinic-based children with ADHD had more physical/developmental problems, more severe functional impairments and teacher-reported hyperactivity/impulsivity symptoms, and higher family burdens than their community counterparts. Our findings suggest that a higher maternal educational level, parent’s perceived child functional impairment, teacher’s perceived impaired peer relationship and hyperactivity-impulsivity, and child physical and developmental problems may be related to the psychiatric referrals of children with ADHD.