Background: Studies on the association between body mass index (BMI) and death risk among patients with hypertension are limited, and the results are inconsistent. We investigated the association between BMI and cardiovascular disease (CVD) and all-cause mortality among hypertensive patients in a population of Beijing, China. Methods: We conducted a prospective cohort study of 2535 patients with hypertension aged 40 to 91 years from Beijing, China. Participants with a history of CVD at baseline were excluded from analysis. Cox proportional hazards regression models were used to estimate the association of different levels of BMI stratification with CVD and all-cause mortality. Results: During a mean follow-up of 8.1 years, 486 deaths were identified, including 233 cases of CVD death. The multivariable-adjusted hazards ratios for all-cause mortality associated with BMI levels (<20, 20-22, 22-24, 24-26 [reference group], 26-28, 28-30, and >= 30 kg/m(2)) were 2.03 (95% confidence interval [CI], 1.48-2.78), 1.61 (95% CI, 1.18-2.20), 1.30 (95% CI, 0.95-1.78), 1.00 (reference), 1.12 (95% CI, 0.77-1.64), 1.33 (95% CI, 0.90-1.95), and 1.66 (95% CI, 1.10-2.49), respectively. When stratified by age, sex, or smoking status, the U-shaped association was still present in each subgroup (P > 0.05 for all interactions). Regarding the association of BMI with CVD mortality, a U-shaped trend was also observed. Conclusions: The present study showed a U-shaped association of BMI with CVD and all-cause mortality among patients with hypertension. A lowest risk of all-cause mortality was found among hypertensive patients with BMI between 24 and 26 kg/m(2).