OBJECTIVES: There is very limited existing research on national-level racial/ethnic disparities in overall prescription drug utilization and out-of-pocket prescription drug (OOP PD) expenditures in working-age adults. This analysis used the 2002 Medical Expenditure Panel Survey (MEPS) to study pharmaceutical use and OOP PD expenditure differences across racial/ethnic groups, in a nationally representative population of Asian, Black, Hispanic and White adults age 18-64. METHODS: The predisposing, enabling, and need framework of the Andersen Behavioral Model of Health Services Utilization was used to guide hypotheses and variable selection. MEPS is a national survey of health care use, expenditures, sources of payment, and insurance coverage. A negative binomial regression model was used to analyze the number of annual prescriptions and a two-part model was used to model annual OOP PD expenditures. These models adjusted for various demographic, health status, income and insurance coverage variables. RESULTS: In unadjusted analyses, Whites filled an average of 10.1 medicines in 2002; this was significantly greater than drug use for Hispanics (4.72), Blacks (8.55) and Asians (4.1), p-value<0.05 for all comparisons. After adjusting for predisposing, enabling and need factors, statistically significant differences in levels of medication use across racial/ethnic groups remained: compared to Whites, Asians used 47.8%, Blacks 26.2% and Hispanics 39.1%, fewer prescription drugs per year. In unadjusted analyses, Whites had OOP costs of $218, compared to $110, $163, and $75 for Hispanics, Blacks, and Asians, respectively. After adjustment, among subjects with any drug expenditures, these racial/ethnic groups had 38%, 30% and 56% lower expenditures compared to Whites, respectively. CONCLUSION: This study found significant disparities in pharmaceutical use across racial/ethnic groups, even after controlling factors such as income, insurance coverage and health status. Pharmaceutical therapy is critical to healthcare and lower utilization among minorities may explain why these groups suffer disproportionately from the effects of chronic diseases.