Increasingly, clinical, pharmaceutical and translational research studies use patient-reported outcomes as primary and secondary end points. Obtaining this type of information from children themselves is now possible, but effective assessment requires developmentally sensitive conceptual models of child health and an appreciation for the rapid change in children's cognitive capacities. To overcome these barriers, outcomes researchers have capitalized on innovations in modern measurement theory, qualitative methods for instrument development and new computerized technologies to create reliable and valid methods for obtaining self-reported health data among 8-17-year-old children. This article provides a developmentally focused framework for selecting child-report health assessment instruments. Several generic health-related quality of life instruments and the assessment tools developed by the NIH-sponsored Patient-Reported Outcome Measurement Information System network are discussed to exemplify advances in the measurement of children's self-reported health, illness, wellbeing and quality of life.