ABSTRACT. Objective. The aim of treatment for attention-deficit/hyperactivity disorder (ADHD) is to decrease symptoms, enhance functionality, and improve well-being for the child and his or her close contacts. However, the measurement of treatment response is often limited to measuring symptoms using behavior rating scales and checklists completed by teachers and parents. Because so much of the focus has been on symptom reduction, less is known about other possible health problems, which can be measured easily using healthrelated quality-of-life (HRQL) questionnaires, which are designed to gather information across a range of health domains. The aim of our study was to measure HRQL in a clinic-based sample of children who had a diagnosis of ADHD and consider the impact of 2 clinical factors, symptom severity and comorbidity, on HRQL. Our specific hypotheses were that parent-reported HRQL would be poorer in children with ADHD than in normative US and Australian pediatric samples, in children with increasing severity of ADHD symptoms, and in children who had diagnoses of comorbid psychiatric disorders.Methods. Cross-sectional survey was conducted in British Columbia, Canada. The sample included 165 respondents of 259 eligible children (63.7% response rate) who were referred to the ADHD Clinic in British Columbia between November 2001 and October 2002. Children who are seen in this clinic come from all parts of the province and are diverse in terms of socioeconomic status and case mix. ADHD was diagnosed in 131 children, 68.7% of whom had a comorbid psychiatric disorder. Some children had >1 comorbidity: 23 had 2, 5 had 3, and 1 had 4. Fifty-one children had a comorbid learning disorder (LD), 45 had oppositional defiant disorder or conduct disorder (ODD/CD), and 27 had some other comorbid diagnosis. The mean age of children was 10 years (standard deviation: 2.8). Boys composed 80.9% (N ؍ 106) of the sample. We used the 50-item parent version of the Child Health Questionnaire to measure physical and psychosocial health. Physical domains include the following: physical functioning (PF), role/social limitations as a result of physical health (RP), bodily pain/discomfort (BP), and general health perception (GH). Psychosocial domains include the following: role/social limitations as a result of emotional-behavioral problems (REB), self-esteem (SE), mental health (MH), general behavior (BE), emotional impact on parent (PTE), and time impact on parents (PTT). A separate domain measures limitations in family activities (FA). There is also a single-item measure of family cohesion (FC). Individual scale scores and summary scores for physical (PhS) and psychosocial health (PsS) can be computed. Symptom severity data (parent and teacher) came from the Child/Adolescent Symptom Inventory 4. These checklists provide information on symptoms for the 3 ADHD subtypes (inattentive, hyperactive, and combined). Each child underwent a comprehensive psychiatric assessment by 1 of 4 child psychiatrists. Documentation included a full 5-ax...