This study investigated the period of time that blood pressure (BP) should be measured at home in older patients in order to obtain steady BP values. Thirty-six men and 38 women (> or =60 years) were recruited at one family practice. At one office visit the family physician measured supine, sitting and standing BPs three times consecutively in each position. During 10 consecutive days, BP was measured at home five times daily. The supine and standing BPs were measured once in the morning and in the evening and the sitting BP once at noon. These home BP values were averaged over the first day (1-day), over the first 3 days (3-day) and all 10 days (10-day) of measurements. In both the supine (-5.1 mm Hg) and sitting (-3.8 mm Hg) positions the 10-day average systolic home BP was significantly lower than the corresponding office BP. The opposite was observed for the 10-day average standing home BP values (+7.3/+3.4 mm Hg). Comparison of the 3-day and 10-day average home BP values showed only a significantly lower 10-day than 3-day systolic BP level in the supine position (-1.1 mm Hg, 95% CI -1.9 to -0.2 mm Hg). Repeated measures ANOVA, showed a small but significant decrease over time only for the supine systolic home BP (-0.29 mm Hg per day, 95% CI -0.49 to -0.08 mm Hg per day). We conclude that in older subjects, 3 days of home measurements may suffice to obtain steady values for the sitting and standing BPs. A longer interval might be required for the supine BP.