Many studies have assessed short-term effects of weight loss on blood pressure, whereas little attention has been paid to long-term effects. We conducted a systematic review to evaluate the long-term effects of weight loss on hypertension outcome measures in adults using literature published from 1966 to 2001. All prospective studies and trials, performed on participants with body mass index of > or =28 kg/m2 with a follow-up of >2 years and weight changes recorded, were included. The data from these studies were used to model the long-term effects on blood pressure. Previous reviews on shorter-term studies indicate a 1:1 drop in blood pressure (mm Hg) with weight loss (kilograms). Our findings, based on studies with follow-up of > or =2 years, demonstrate blood pressure decreases less than this after weight loss. The surgical intervention studies exhibited huge weight losses with undramatic blood pressures changes. When surgical interventions are excluded, the models suggest that for 10 kg weight loss, decreases of 4.6 mm Hg and 6.0 mm Hg in diastolic and systolic blood pressure, respectively, may be expected, about half of that predicted from the short-term trials. Initial blood pressure, the length of follow-up, medication changes, and physiological restrictions may contribute to this reduced effect in the long-term studies. Extrapolation of short-term blood pressure changes with weight loss to the longer term is potentially misleading. The weight/hypertension relationship is complex and needs well-conducted studies with long-term follow-up to examine the effects of weight loss on hypertension outcomes.