Population-based disease management should be enhanced by good risk assessment models and instruments. We prospectively evaluated the ability of a simple measure of short-term asthma control (scored 0 to 4) to predict asthma 12-mo health care utilization (HCU). A total of 5,172 adult asthma patients completed a brief questionnaire in fall 1997 to assess current level of asthma control. We then evaluated HCU for calendar year 1998. Ninety-three percent had health plan eligibility in 1998 and were included in this analysis. Both acute and routine asthma utilization increased with increasing numbers of asthma control problems. Rates of acute care episodes were 3.5 (95% confidence interval [CI] = 2.9, 4.3) times more likely for those with 3 to 4 control problems versus those with no control problems. Lesser, but statistically significant, increases were seen for those with two (relative risk [RR] = 1.7, 95% CI = 1.4, 2.2) or one (RR = 1.4, 95% CI = 1.1, 1.8) control problems. These patterns were similar for men and women, and diminished with increasing age. The asthma control index contributed significantly to prospective prediction models even after adjusting for administrative data such as medication use and prior HCU. These data reinforce the usefulness of measures of short-term asthma control both for the individual clinician and for those interested in population-based asthma management.