According to official recommendations, indirect blood pressure (BP) measurement should be performed in the brachial artery at heart level in the seated position. At lower levels the hydrostatic pressure of the column of blood in between the heart and the point of measurement is added. The clinical relevance of deviations from the recommendations was investigated in a population-based sample of 401 healthy men and women of ages 15-84 years. In the seated position, the systolic BP measured with the upper arm parallel to the sternum was higher than that with the forearm elevated at heart level. The difference was 9.4 (SD 6.6) mm in men and 8.2 (6.9) mm in women. The corresponding differences in diastolic BP were 13.6 (4.4) mm in men and 12.4 (4.5) mm in women. At heart level, the supine systolic BP was 7.9 (7.5) mm higher than the seated in men, and 8.2 (8.0) mm higher in women, while the diastolic BP was the same up to the age of 40. It is concluded that deviations from the recommended body position and arm level are clinically relevant. The pattern of discrepancy, falsely high BPs below the heart level and a higher pulse pressure in the supine position, is uniform in both sexes at all adult ages.