Medication adherence is a significant problem in patients with rheumatoid arthritis (RA), a prevalent autoimmune disease. Because of the equivocal results reported in the research, consistent predictors of medication adherence in patients with RA are undetermined. A cross-sectional descriptive, predictive study of 108 patients with RA was used to: (1) describe self-reported medication adherence to disease-modifying anti-rheumatic drugs (DMARDs); (2) compare demographic (age, residence, marital status, employment status, years of education, and ethnicity) and clinical (duration of disease and number of medications) factors of adherent and nonadherent individuals; and (3) determine the predictive power of demographic and clinical factors for DMARD adherence using various cut-points (research-based, mean, and median) on a validated, self-report scale measuring medication adherence. Independent samples t-tests, Chi-square analyses, and logistic regression modeling were used to analyze these data. Approximately 90% of the individuals with RA reported adherence with their prescribed DMARD prescriptions. The only demographic and clinical difference between the adherent and nonadherent group was ethnicity (P = 0.04); non-Caucasian individuals reported significantly less adherence with their prescribed DMARDs when compared with Caucasian individuals. Logistic regression models identified ethnicity (OR = 3.34–10.1; P<0.05) and the number of medications taken (OR = 1.7; P<0.05) as predictors of medication nonadherence. These data provide evidence that ethnicity and taking an increased number of prescribed medications are independent predictors of medication adherence in patients with RA. These findings confirm the presence of a health disparity and an area in which further research is needed to optimize patient outcomes. Drug Dev Res 72:756–763, 2011. © 2011 Wiley Periodicals, Inc.