BACKGROUND: Insufficient blood pressure control is a frequent problem despite the existence of effective treatment. Insufficient adherence to self-monitoring as well as to therapy is a common reason. Blood pressure self-measurement at home (Home Blood Pressure Measurement, HBPM) has positive effects on treatment adherence and is helpful in achieving the target blood pressure. Only a few studies have investigated whether adherence to HBPM can be improved through simple measures resulting also in better blood pressure control. OBJECTIVE: Improvement of self-monitoring and improved blood pressure control by using a new colour-coded blood pressure diary. OUTCOME: Primary outcome: Change in systolic and/or diastolic blood pressure 6 months after using the new colour-coded blood pressure diary.Secondary outcome: Adherence to blood pressure self-measurement (number of measurements/entries). METHODS/DESIGN: Randomised controlled study.Population: 138 adult patients in primary care with uncontrolled hypertension despite therapy. The control group uses a conventional blood pressure diary; the intervention group uses the new colour-coded blood pressure diary (green, yellow, red according a traffic light system). EXPECTED RESULTS/CONCLUSION: The visual separation and entries in three colour-coded areas reflecting risk (green: blood pressure in the target range <or= 140/<or= 90 mmHg, yellow: blood pressure >140/>90 mmHg, red: blood pressure in danger zone > 180 mmHg/>110 mmHg) lead to better self-monitoring compared with the conventional (non-colour-coded) blood pressure booklet. The colour-coded, visualised information supports improved perception (awareness and interpretation) of blood pressure and triggers correct behaviour, in the means of improved adherence to the recommended treatment as well as better communication between patients and doctors resulting in improved blood pressure control. TRIAL REGISTRATION: ClinicalTrials.gov ID NCT01013467.