OBJECTIVES: To determine the effect of enrollment in a prescription drug plan on use of controller medications in patients with persistent asthma METHODS: The study used a retrospective, cross sectional research design. The data source utilized was the 2008 Medical Expenditure Panel Survey (MEPS), a nationally representative sample of the non-institutionalized, civilian U.S. population. Analysis was restricted to asthma patients who reported use of more than 3 canisters of rescue inhalers in a three-month period. Controller medication use was self-reported by MEPS respondants. Descriptive statistics was used to describe the sample and their controller medication use. A logistic regression model was used to assess the effect of prescription drug coverage based on the type of prescription drug plan on the controller medication use while adjusting for age, gender, race, ethnicity, income and perceived health status. All analyses were carried out using SASv.9.1.  RESULTS: Forty-two percent of respondents had prescription drug coverage while 67% reported use of controller medications. In the regression model,  controller medication use was found to be similar amongst patients with prescription drug coverage and patients without coverage (68%, 66%, respectively). Patients with prescription drug coverage  were less likely to use controller medications than those who did not have coverage, although this effect was not significant (OR=0.53,CI:0.28-1.01). Patients with Medicare (OR=4.35, CI:1.61-11.75), Medicaid (OR=5.44, CI:2.23-13.24) or Veterans Affairs (OR=12.82, CI:3.21-51.16) prescription coverage were more likely to use controller medications when compared with patients in other types of plans. Both pediatric patients (OR=5.51, CI:1.27-23.88) and patients with excellent perceived health status (OR=5.10, CI:2.04-12.76) had a higher likelihood of using controller medications.  CONCLUSIONS: Enrollment in a prescription drug plan did not show a significant impact on use of controller medications. However, enrollment in Medicare, Medicaid or Veterans Affairs prescription plans increased likelihood of controller medication use in this patient cohort.