OBJECTIVES: To evaluate the efficacy of a healthcare education program for patients with hypertension. METHODS: A multicenter, prospective, cluster-randomized trial was conducted. Randomization was by primary care center; 18 of 36 urban primary care centers in Barcelona and its metropolitan area were randomized to the intervention group (IG) and 18 to the control group (CG). The study sample consisted of patients with hypertension (n=996; 515 in the IG and 481 in the CG) receiving outpatient treatment with antihypertensive drugs. The intervention consisted of personalized information by a trained nurse and written leaflets. Questionnaires on knowledge and awareness of hypertension and its medication, treatment adherence, healthy lifestyle habits, systolic and diastolic blood pressure, and body mass index were assessed at each visit, with a 12-month follow-up. An intention-to-treat analysis was applied. RESULTS: Knowledge of hypertension increased by 27.8% in the IG and by 18.5% in the CG, while that of medication increased by 10.1% in the IG and 5.5% in the CG. Treatment adherence measured by the Morisky-Green test increased by 9.6% (95% CI: 5.5-13.6) in the IG and 8.8% (95% CI: 4.9-12.6) in the CG. There were no differences in adherence on the other tests used. No differences were observed between the IG and CG in clinical variables such as blood pressure or BMI at the end of the trial. CONCLUSIONS: The educational intervention had no significant impact on patients' adherence to the medication.