Abstract Introduction: This study examines incident treatment patterns for attention-deficit/hyperactivity disorder (ADHD) in children seen in eight integrated healthcare delivery systems and identifies factors associated with adherence to Healthcare Effectiveness Data and Information Set (HEDIS) quality measures developed by the National Committee for Quality Assurance (NCQA). Method: A retrospective cohort analysis using electronic healthcare data from children aged 3 through 17 years with newly diagnosed ADHD between January 1, 2009 and December 31, 2010 was conducted. NCQA quality definitions for initiation and for continuation and maintenance (C&M) of ADHD medications were expanded to include preschoolers and adolescents. Poisson regression models with robust error variance were used to evaluate the association between NCQA HEDIS adherence measures, provider type, patient characteristics and care process measures. Results: Of 6864 children aged 3-17 years old qualifying for incident treatment analyses, 5538 (80.7%) were started on ADHD medication within a year of diagnosis. Adherence to NCQA HEDIS measures was 49.8% for initiation and 45.8% for C&M, with adherence rates higher for mental health than non-mental health providers, school-aged children than adolescents, and for patients concurrently on other psychotropic medications than those who were not. Of those started on ADHD medication, 62.3% were not eligible for C&M analyses according to HEDIS guidelines, because they did not receive continuous (210 of 300 days) ADHD medication treatment, with adolescents less likely than school-aged children to persist with medications. Conclusion: Study limitations must be considered, including reliance on electronic medical record data, absence of patient race and sociodemographic data, and limited generalizability to other care contexts. Nevertheless, findings suggest novel strategies are needed to improve the quality of ADHD care processes for children of all ages, because even within integrated delivery systems less than half of children with ADHD received care consistent with NCQA HEDIS standards for initiation and C&M care. Results suggest the need to refine quality measures by including follow-up care in those children not receiving or discontinuing medication treatment, a considerable quality concern not currently captured in NCQA HEDIS standards.