The evidence relating obesity measured with body mass index (BMI) in the elderly to late-onset Alzheimer disease (LOAD) is conflicting. Central obesity in middle age is related to a higher risk of LOAD, but data in the elderly are lacking. We explored whether measures of central obesity, waist circumference, and waist to hip ratio (WHR) were better predictors of LOAD compared with BMI in the elderly. Participants were 1459 persons aged 65 years and older without dementia at baseline, with follow-up, and with anthropometric data from a longitudinal study of aging in New York City. Proportional hazards regression was used for multivariable analyses relating BMI, waist circumference, and WHR to LOAD. There were 145 cases of Alzheimer disease in 5734 person-years of follow-up. Only WHR was related to higher LOAD risk (hazard ratio of the fourth quartile compared with the first=2.5; 95% confidence interval=1.3, 4.7) after adjustment for age, sex, education, ethnic group, Apolipoprotein E-ε4, type 2 diabetes, hypertension, non-high-density lipoprotein-cholesterol, high-density lipoprotein cholesterol, and stroke. Our results support the notion that central obesity is related to a higher risk of LOAD.