['To examine if the body mass index (BMI) in midlife is related to cognitive function 30 years later in a dementia-free sample.', 'BMI was reported in 1963 at age 50-60 years, and cognitive abilities were examined 30 years later in a longitudinal design with 5 measurement occasions at 2-year intervals (n = 417). The cognitive abilities examined included tests of long-term memory, short-term memory, speed, verbal and spatial ability.', 'Multilevel modeling adjusting for demographic and lifestyle factors, and relevant diseases showed that a higher BMI in midlife predicted lower test performance 30 years later. Significant associations between BMI and level of performance were found in all cognitive abilities; however, a higher midlife BMI was not associated with steeper cognitive decline.'] Is overweight in midlife related to lower cognitive function 30 years later : a prospective study with longitudinal assessments?