Objective: To relate measured obesity duration in mid-life with subsequent incidence of physical disability over and above body mass index (BMI) attained. Methods: Framingham Offspring Study is a longitudinal study that began in 1971. Examination 5 (1991-1995; ?baseline?) and disability onset ascertained from examinations 6-8 (2008) were used. About 2,095 disability-free participants aged 45-65 years at baseline were included. Obesity (BMI 30 kg/m2) durationwas calculated between examination 1 and examination 5. Cox regression was used to analyze time to disability. Results: 204 participants developed disability (incidence rate 5 7.9 per 1,000 person-years). Obesity duration ranged from 0 to 22 years (mean of 2.0 years overall, 8.3 years for those with baseline obesity). Obesity duration increased risk of new disability (hazard ratio [HR] 1.07 per year of obesity; 95 confidence interval [CI] 1.05-1.09). This association was attenuated on further adjustment for baseline BMI (HR 1.03; 95 CI 1.00-1.06). Conclusions: Being obese for longer during mid-life increases the risk of later-life disability over and above attained BMI. These results support the need for prevention of weight gain in young adults to avoid an increasing burden of physical disability in later life.