BACKGROUND: The relationship between asthma controller medication use and exacerbation rates over time is unclear at the population level. OBJECTIVE: To estimate the change in asthma controller medication use between 2 time periods as measured by the controller-to-total asthma medication ratio and its association with changes in asthma exacerbation rates between 1997-1998 and 2004-2005. METHODS: The study design was a cross-sectional population-level comparison between individuals from 1997-1998 and 2004-2005. Study participants were individuals aged 5 to 56 years identified as having asthma in the Medical Expenditure Panel Survey (MEPS). The main outcome measures were a controller-to-total asthma medication ratio greater than 0.5 and asthma exacerbation rates (dispensing of systemic corticosteroid or emergency department visit/hospitalization for asthma) in 1997-1998 compared with 2004-2005. RESULTS: The proportion of individuals with a controller-to-total asthma medication ratio greater than 0.5, when adjusted for other demographic factors, has improved by 16.1% (95% CI: 10.8%, 21.3%) for all individuals from 1997-1998 to 2004-2005. Annual asthma exacerbation rates did not change significantly in any group from 1997-1998 to 2004-2005 (0.27/year to 0.23/year). African American and Hispanic individuals with asthma had higher asthma exacerbation rates and a lower proportion with a controller-to-total asthma medication ratio greater than 0.5 than whites in both 1997-1998 and 2004-2005; however, these differences were not statistically significant. CONCLUSIONS: An increase in asthma controller-to-total medication ratio in a sample reflective of the US population was not associated with a decreased asthma exacerbation rate comparing 1997-1998 and 2004-2005.