Objectives. This study examined whether body mass index (BMI) or change in BMI raises the risk of disability in adulthood. Methods. The relation between BMI and upper- and lower-body disability was examined among adult subjects from a national longitudinal survey (n = 6833). Tobit regression models were used to examine the effect of BMI on disability 10 and 20 years later. Results. Obesity (BMI≥30) at baseline or becoming obese during the study was associated with higher levels of upper- and, especially, lower-body disability. In persons who began the study with a BMI of 30 or more and became normal weight, disability was not reduced. Underweight persons (BMI < 18.5) also manifested higher disability in most instances. Conclusions. Disability risk was higher for obese persons, but overweight was not consistently associated with higher disability.