Asthma is both common and costly. Neither the risk factors of poor outcome nor the predictors of better outcome are well understood. Illness severity is clearly an important predictive factor in asthma, but may explain less variability in outcome than other determinants, such as patient-perceived asthma control, other asthma-related psychosocial measures, and the kind and extent of subspecialty care for asthma. By quantifying predictors of asthma-specific quality of life, functional status, services utilization, and the direct and indirect illness costs of asthma, this study addressed a major research gap in secondary and tertiary prevention efforts.