The association between body adiposity at older ages and the development of cognitive impairment is unclear.The association of body mass index (BMI) and waist circumference in late life with incidence of cognitive impairment was prospectively examined in a cohort study of 1,351 Latinos, aged 60-101 and residents of the Sacramento, CA, area at study baseline. The status of dementia and "cognitive impairment but not demented" (CIND) was determined at baseline and at each of five follow-up examinations by a multistage assessment protocol. Incident cases of dementia and CIND were combined (dementia/CIND) for more than 8 years of follow-up. BMI was categorized as less than 25.0, 25.0-29.9 (overweight), and 30 kg/m(2) or greater (obese). Waist circumference was categorized into sex-specific tertiles.Dementia/CIND was diagnosed in 110 (8.2%) participants. Compared with the lowest BMI category, overweight participants had a 48% decreased rate of dementia/CIND (adjusted hazard ratio [HR] = 0.52, 95% confidence interval [CI]: 0.30-0.91) and obese participants had a 61% decreased rate of dementia/CIND (HR = 0.39, 95% CI: 0.20-0.78). Rates of dementia/CIND for the middle and high tertile of waist circumference, compared with the low tertile, were 80% and 90% higher, respectively (adjusted HR = 1.8, 95% CI: 1.1-3.1, and adjusted HR = 1.9, 95% CI: 0.91-3.8).Abdominal fat in late life appears to confer an increased risk for dementia/CIND, whereas overall obesity appears to be protective. This may reflect age-related changes in body composition and the association of visceral fat with metabolic dysregulation.