© The Author 2014. Background: Compared with adults without type 2 diabetes mellitus, those with the disease experience more limitations in their physical functioning (PF). Look AHEAD is a large multicenter trial that examined the effects of an intensive lifestyle intervention (ILI) for weight loss on cardiovascular outcomes compared with diabetes support and education (DSE). Although the current study compared treatment differences between ILI and DSE on PF, the primary goal was to examine whether this effect was moderated by age and history of cardiovascular disease at enrollment. Methods: Overweight or obese adults with type 2 diabetes mellitus (n = 5,145) were randomly assigned to either ILI or DSE. The mean (±SD) age and % females in ILI was 58.9 years (±6.9) and 59.8%; it was 58.6 years (6.8) and 59.5% in DSE. Analysis in 4,998 participants assessed the differential rates of decline in PF across a period of 8 years for the ILI and DSE groups. Results: ILI resulted in improved PF compared with DSE after 1 year (p <.0001) and was maintained across time. Within the ILI, older adults experienced greater improvements than younger adults (p <.0001). By year 2, persons in ILI with preexisting cardiovascular disease were no different in PF than in DSE participants with preexisting cardiovascular disease. Conclusion: With the exception of persons who had a history of cardiovascular disease, ILI slowed the decline in PF with type 2 diabetes mellitus despite weight regain, an effect that was stronger for older than younger participants and could translate into reductions in falls and disability.