OBJECTIVES: To examine the relationship between self-reported health status, prophylactic medication utilization, and health care service utilization in older adults with asthma. METHODS: Design: A prospective longitudinal cohort study was conducted over a 2-year post-enrollment period in a population of managed care enrolled asthmatic older adults. Patients completed a comprehensive health risk screen at time of enrollment in the plan. Setting: A Medicare HMO in the Southeastern United States with prescription benefit. Participants: A total of 129 Medicare-HMO enrolled older adults with asthma using inhaled corticosteroid therapy as prophylaxis were available for complete follow up. Measurements: We measured self-reported health perception, falls, lifestyle, depressive symptomatology, and pre-enrollment health care service use using a comprehensive risk screen. We used the medication possession ratio and total annual health care charges as measures of post-enrollment inhaled corticosteroid and health care service use. RESULTS: After adjusting for the effects of other variables we found that depressive symptomatology (DS) at baseline and increased comorbidity severity (using the Charlson comorbidity index) were associated with significant reductions in prophylactic medication possession (27% with DS, and 6% with unit increase in Charlson's index, p<0.05). Additionally we found, after adjusting for the effects of baseline health status, a 10% increase in prophylactic medication possession was associated with a 5% decrease in total annual health care charges in this population (p<0.05). CONCLUSIONS: There seem to be strong associations between poor health status at time of enrollment, decreased post-enrollment prophylactic medication use and increased post-enrollment health care service utilization in older adults with asthma.