Obesity has been shown to be associated with hypertension in Africa, the Caribbean, and the United States, but there has not previously been an opportunity to compare the magnitude of this relation and estimate the contribution of obesity to hypertension risk across these populations. The International Collaborative Study on Hypertension in Blacks (ICSHIB) used age-stratified sampling and a standardized protocol to measure blood pressure and hypertension risk factors. We analyzed data on 9,102 men and women, age 25-74 years, from seven sites. We studied hypertension (140/90 mmHg or medication) in relation to body mass index (BMI) and sex-specific BMI cut-points designating "overweight" and "obesity." The prevalence of these conditions ranged from 6% to 63% for overweight, from 1% to 36% for obesity, and from 12% to 35% for hypertension. Adjusted relative risks were similar in most sites, ranging from 1.3 to 2.3 for both cut-points. We found that 6-29% of hypertension in each population was attributable to overweight and 0-16% to obesity. Comparing rural Africa with the United States, 43% of the difference in hypertension prevalence for women was attributable to overweight, and 22% for men, whereas respective values for obesity were 14% and 11%. These results indicate that the association between adiposity and hypertension is roughly constant across a range of environments, with little evidence for variation in susceptibility to effects of overweight in these groups.