This article reviews the recommended techniques for accurate and reproducible blood pressure measurements. The scientific basis underlying current recommendations for blood pressure measurement is presented. Many of the current recommendations are not followed in ambulatory care clinics and this paper will show how measurement errors in excess of 15 mm Hg or more can occur. Many patients will be misclassified and treated inappropriately when errors in blood pressure measurement of this magnitude are made. Rigorous adherence to proper blood pressure measurement is necessary to evaluate a patient's risk of cardiovascular disease, and to assess the need or efficacy of antihypertensive therapy.