This paper describes the association between longitudinal changes in blood pressure and changes in measures of ponderosity. Between 1971 and 1981, 2,925 Muscatine, Iowa schoolchildren were measured at least once between ages 6 and 15 years and again between ages 15 and 18. The study shows that change in ponderosity is associated with change in blood pressures; children whose ponderosity decreases relative to their peers usually exhibit a similar drop in their systolic and diastolic blood pressures, while children who gain in ponderosity show a similar gain in their blood pressures. The magnitude of change in blood pressure is related to amount of ponderosity gain or loss and does not depend on initial blood pressure. These data suggest that for obese children weight loss might be an effective method for reducing their blood pressure.