Objective: The purpose of this study was to assess the effectiveness of a quality improvement (QI) plan aimed at primary healthcare teams (PHCTs) to optimise hypertension control and to compare it with standard clinical care. Methods: Design Multicentric, non-randomised, quasi-experimental controlled intervention study. Setting 5 PHCTs in the intervention and 13 in the standard care group in the province of Barcelona, Catalonia, Spain. Participants This is a population-based study in which all patients over 18 years of age with a diagnosis of hypertension before 1 January 2006 were included (n=9877 in the intervention group and n=21 704 in the control group). Intervention A QI plan that targeted primary care professionals. The plan included training sessions, implementation of recommended clinical practice guidelines for the management of hypertensive patients and audit and feedback to health professionals. Main outcome measure Prevalence of hypertensive patients with an adequate blood pressure (BP) control. Results: The adjusted difference between intervention and standard care groups in the odds of BP control was 1.3 (95% CI 1.1 to 1.6, p=0.003). Results of the mixed model on repeated measures showed that, on average, an individual in the intervention group had an increase of 92% in the odds of BP control (OR 1.9, 95% CI 1.7 to 2.1). Conclusions: The implementation of a QI plan can improve BP control. This strategy is potentially feasible for up-scaling within the existing PHCTs. Trial registration: ClinicalTrials.gov MS: 1998275938244441.