Background: There are scant data on the effect of body mass index (BMI) (calculated as weight in kilograms divided by the square of height in meters) on cardiovascular events and death in older patients with hypertension. Objective: To determine if low body mass in older patients with hypertension confers an increased risk of death or stroke. Patients: Participants were 3975 men and women (mean age, 71 years) enrolled in 17 US centers in the Systolic Hypertension in the Elderly Program trial, a randomized, doubleblind, placebo-controlled clinical trial of low-dose antihypertensive therapy, with follow-up for 5 years. Main Outcome Measures: Five-year adjusted mortality and stroke rates from Cox proportional hazards analyses. Results: There was no statistically significant relation of death or stroke with BMI in the placebo group (P = .47), and there was a U- or J-shaped relation in the treatment group. The J-shaped relation of death with BMI in the treated group (P = .03) showed that the lowest probability of death for men was associated with a BMI of 26.0 and for women with a BMI of 29.6; the curve was quite fiat for women across a wide range of BMIs. For stroke, men and women did not differ, and the BMI nadir for both sexes combined was 29, with risk increasing steeply at BMIs below 24. Those in active treatment, however, had lower death and stroke rates compared with those taking placebo. Conclusions: Among older patients with hypertension, a wide range of BMIs was associated with a similar risk of death and stroke; a low BMI was associated with increased risk. Lean, older patients with hypertension in treatment should be monitored carefully for additional risk factors.