Pediatric patients' self-report of health-related quality of life (HRQOL) has emerged as an important patient-based health outcome. A practical, validated generic measure of HRQOL facilitates assessing risk, tracking health status, and measuring treatment outcomes in pediatric populations. The PedsQL is a brief, standardized, generic assessment instrument that systematically assesses patients' and parents' perceptions of HRQOL in pediatric patients with chronic health conditions using pediatric cancer as an exemplary model. The PedsQL is based on a modular approach to measuring HRQOL and consists of a 15-item core measure of global HRQOL and eight supplemental modules assessing specific symptom or treatment domains. The PedsQL was empirically derived from data collected from 291 pediatric cancer patients and their parents at various stages of treatment. Both reliability and validity were determined. Cronbach's alpha coefficients for the core measure (alpha = .83 for patient and alpha = .86 for parent) were acceptable for group comparisons. Alphas for the patient self-report modules generally ranged from .70 to .89. Discriminant or clinical validity, using the known-groups approach, was demonstrated for patients on- versus off-treatments. The 11 scales showed small-to-medium positive intercorrelations, supporting the multidimensional measurement model. Further construct validity was demonstrated via a multimethod-multitrait matrix using standardized psychosocial questionnaires. The results support the PedsQL as a reliable and valid measure of HRQOL. The PedsQL core and modular design makes it flexible enough to be used in a variety of research and clinical applications for pediatric chronic health conditions.