Purpose: This study has two purposes. First, it determines if there is a relationship between body weight and the onset of functional impairment across time among this sample of older adults. More specifically, it examines if obese older adults are more likely to experience the onset of functional impairment. Second, it explores how health behaviors and health conditions may explain the relationship between body weight and the onset of functional impairment. Design and Methods: With the use of longitudinal data from the Asset and Health Dynamics Among the Oldest Old (AHEAD) survey, logistic regression models on the onset of functional impairment over two time points are estimated for older adults. Results: Results indicate that body weight (more specifically being overweight or obese) makes one more likely to experience the onset of functional impairment across various domains of impairment. Outside of health behaviors and health conditions, obesity has an independent effect on the onset of impairment in strength, lower body mobility, and activities of daily living. Implications: Study findings support the active treatment of weight problems in older adults. Future directions for research in this area should address effective weight management interventions targeting issues related to older individuals.Key Words: Obesity, Overweight, Functional impairment, Health conditions