To examine correlates of guideline adherence in a population with access to health care and prescription drug benefits, the authors conducted a cross-sectional analysis among 5789 patients undergoing hypertension treatment with a single medication in a large New England managed care organization. Logistic regression was used to determine correlates of adherence, defined as use of diuretics or beta blocker as antihypertensive monotherapy during the 1-year study period. Women were more likely than men to receive guideline-adherent therapy (odds ratio [OR], 1.63; 95% confidence interval [CI], 1.45-1.85). Compared with patients covered by health maintenance organization plans, Medicare coverage was positively associated with guideline adherence (OR, 1.38; 95% CI, 1.13-1.69), but fee-for-service coverage was negatively associated (OR, 0.66; 95% CI, 0.48-0.91). Patient age was not a significant correlate of adherence to guidelines (OR, 1.01; 95% CI, 0.94-1.09). Understanding these observations may lead to strategies to improve guideline adherence and reduce health care disparities.