BACKGROUND Accurate blood pressure (BP) readings and correctly interpreting the obtained values are of great importance. However, there is considerable variation in the different BP measuring methods suggested in guidelines and used in hypertension trials. OBJECTIVE To compare the different methods used to measure BP; measuring once, the method used for a large study such as the UKPDS, and the methods recommended by various BP guidelines. METHODS In 223 patients with type 2 diabetes from five family practices BP was measured according to a protocol to obtain the following data: A = first reading, B = mean of two initial readings, C = at least four readings and the mean of the last three readings with less than 15% coefficient of variation difference, D = mean of the first two consecutive readings with a maximum of 5 mm Hg difference. Mean outcomes measure is the mean difference between different BP measuring methods in mm Hg. RESULTS Significant differences in systolic/diastolic BP were found between A and B [mean difference (MD) systolic BP 1.6 mm Hg, P < 0.001], B and C (MD 5.7/2.8 mm Hg, P < 0.001), B and D (MD 6.2/2.8 mm Hg, P < 0.001), A and C (MD 7.3/3.3 mm Hg), and A and D (MD 7.9/3.0 mm Hg, P < 0.001). CONCLUSION Different methods to assess BP during one visit in the same patient lead to significantly different BP readings and can lead to overestimation of the mean BP. These differences are clinically relevant and show a gap between different methods in trials, guidelines and daily practice.