The PedsQL is a modular instrument designed to measure health-related quality of life (HRQOL) in children and adolescents ages 2-18. The PedsQL 4.0 Generic Core Scales were developed to be integrated with the PedsQL Disease-Specific Modules. The PedsQL3.0 Asthma Module was designed to measure pediatric asthma-specific HRQOL. The PedsQL was administered to 529 families. Internal consistency reliability was demonstrated for the PedsQL 4.0 Total Score (alpha = 0.90 child, 0.91 parent report) and Asthma Module (average alpha = 0.71 child, 0.86 parent report). The PedsQL 4.0 distinguished between healthy children and children with asthma. The validity of the PedsQL Asthma Module was demonstrated through intercorrelations with a previously standardized asthma disease- specific instrument. Responsiveness was demonstrated through patient change over time as a result of clinical intervention. The results demonstrate the reliability, validity, and responsiveness of the PedsQL required for an outcome measure in pediatric asthma clinical trials and research.