Purpose: We present final outcomes from the multiple-component Fit and Strong! intervention for older adults with lower extremity osteoarthritis. Design and Methods: A randomized controlled trial compared the effects of this exercise and behavior-change program followed by home-based reinforcement (n = 115) with a wait list control (n = 100) at 2, 6, and 12 months. Fit and Strong! combined flexibility, aerobic walking, and resistance training with education and group problem solving to enhance self-efficacy for exercise and maintenance of physical activity. All participants developed individualized plans for long-term maintenance. Results: Relative to controls, treatment participants experienced statistically significant improvements in self-efficacy for exercise (p = 0.001), minutes of exercise per week (p = 0.000), and lower extremity stiffness (p = 0.018) at 2 months. These benefits were maintained at 6 months and were accompanied by increased self-efficacy for adherence to exercise over time (p =0.001), reduced pain (p = 0.040), and a marginally significant increase in self-efficacy for arthritis pain management (p = 0.052). Despite a substantially smaller sample size at 12 months, significant treatment-group effects were maintained on self-efficacy for exercise (p =0.006) and minutes of exercise per week (p = 0.001), accompanied by marginally significant reductions in lower extremity stiffness (p = 0.056) and pain (p = 0.066). No adverse health effects were seen. Effect sizes for self-efficacy for exercise and for maintenance of physical activity were 0.798 and 0.713, and 0.905 and 0.669, respectively, in the treatment group at 6 and 12 months. Implications: This consistent pattern of benefits indicates that this low-cost intervention is efficacious for older adults with lower extremity osteoarthritis.