Objective: The aim of this study is to evaluate fall rates across body mass index (BMI) categories by age group, considering physical performance and comorbidities. Method: In the Osteoporotic Fractures in Men (MrOS) study, 5,834 men aged ≥65 reported falls every 4 months over 4.8 (±0.8) years. Adjusted associations between BMI and an incident fall were tested using mixed-effects models. Results: The fall rate (0.66/man-year overall, 95% confidence interval [CI] = [0.65, 0.67]) was lowest in the youngest, normal weight men (0.44/man-year, 95% CI = [0.41, 0.47]) and greatest in the oldest, highest BMI men (1.47 falls/man-year, 95% CI = [1.22, 1.76]). Obesity was associated with a 24% to 92% increased fall risk in men below 80 (ptrend ≤.0001, p for interaction by age =.03). Only adjustment for dynamic balance test altered the BMI-falls association substantially. Discussion: Obesity was independently associated with higher fall rates in men 65 to 80 years old. Narrow walk time, a measure of gait stability, may mediate the association.