Associations between high body mass index (BMI) and subsequent cognitive decline, reported in elderly averaging below age 75, become less consistent at older ages. We compared the associations of BMI with cognition in moderately old (ages 75–84, N = 154) and oldest-old (85+, N = 93) samples. BMI and cognition were assessed cross-sectionally in cognitively intact elderly (mean age = 84.5, SD = 4.4) male veterans. Regression analyses of three cognitive domains — executive functions/language, attention, and memory—compared relationship with BMI between the moderately old and oldest-old. Higher BMI was associated with relatively poorer executive functions/language performance in the moderately old, while the opposite relationship, higher BMI associated with relatively better performance, was found in the oldest-old. Associations for the other two cognitive domains did not differ significantly between age groups. The reversal of association direction for executive functions/language performance with higher BMI is consistent with the protected survivor model. This model posits a minority subpopulation with a protective factor—genetic or otherwise—against both mortality and cognitive decline associated with risk factor status. The very old who remain cognitively intact despite the presence of risk factors are more likely to possess protection.