BACKGROUND: High blood pressure (BP) is one of the most important risk factors for stroke, and antihypertensive therapy significantly reduces the risk of cardiovascular morbidity and mortality. However, achieving a regulated BP in hypertensive patients is still a challenge. OBJECTIVE: To evaluate the impact of an intervention targeting GPs' management of hypertension. METHODS: A cluster randomized trial comprising 124 practices and 2646 patients with hypertension. In the Capital Region of Denmark, the participating GPs were randomized to an intensive or to a moderately intensive intervention group or to a control group and in Region Zealand and Region of Southern Denmark, practices were randomized into a moderately intensive intervention and to a control group. The main outcome measures were change in proportion of patients with high BP and change in systolic BP (SBP) and diastolic BP (DBP) from the first to the second registration. RESULTS: The proportion of patients with high BP in 2007 was reduced in 2009 by ~9% points. The mean SBP was reduced significantly from 2007 to 2009 by 3.61 mmHg [95% confidence interval (CI): -4.26 to -2.96], and the DBP was reduced significantly by 1.99 mmHg (95% CI: -2.37 to -1.61). There was no additional impact in either of the intervention groups. CONCLUSION: There was no impact of the moderate intervention and no additional impact of the intensive intervention on BP.