BACKGROUND TO DATA REVIEW: Epidemiologic surveys have demonstrated that hypertension is associated with obesity in a substantial proportion of cases, particularly in young and middle-aged adults. Despite the clinical importance of this association the nature of the relationship between body weight and blood pressure remains obscure. CONCLUSION OF DATA REVIEW: The data reviewed here indicate that obesity-related hypertension involves insulin and the sympathetic nervous system, and may be part of a metabolic adaptation to the obese state.