BACKGROUND: Although health-related quality of life (HRQL) has been increasingly used as an outcome in asthma, its utility for identifying patients at risk for adverse asthma outcomes has not been established. OBJECTIVE: In a prospective cohort study, to evaluate the longitudinal impact of HRQL on future health care utilization and cost among adults with asthma, accounting for known risk factors for utilization. METHODS: A stratified random sample of 3,482 adult Northern CA Kaiser Permanente members with asthma was selected using computerized utilization databases and a screening survey item. Subjects completed a mail survey that included measures of generic (SF-12) and asthma-specific HRQL (ITG-Asthma Short Form battery). During the 12 months after survey completion, computerized utilization and cost data were ascertained. RESULTS: Better baseline asthma-specific HRQL was associated with a decreased risk of asthma-related emergency department visit or hospitalization during longitudinal followup (odds ratio per 10-point score increment 0.84; 95% confidence interval [CI] 0.74 to 0.95), controlling for demographic and clinical factors. Better baseline generic physical HRQL was associated with a decreased risk of future all-cause hospitalization (odds ratio 0.68; 95% CI 0.60 to 0.77). More favorable asthma-specific HRQL scores were also related to decreased asthma-related health care costs during the ensuing year (-0.086 log-dollars per 10-point score increment; 95% CI -0.11 to -0.06). Better generic physical HRQL scores were associated with lower total costs (-0.24 log-dollars; 95% CI -0.32 to -0.17). CONCLUSIONS: In a large cohort of adult health maintenance organization members with asthma, asthma-specific HRQL was associated with future asthma-related utilization and cost.