Background The challenge of weight-loss maintenance is well known, but few studies have followed successful weight losers over an extended period or evaluated the effect of behavior change on weight trajectories. Purpose To study the weight-loss trajectories of successful weight losers in the National Weight Control Registry (NWCR) over a 10-year period, and to evaluate the effect of behavior change on weight-loss trajectories. Methods A 10-year observational study of self-reported weight loss and behavior change in 2886 participants (78% female; mean age 48 years) in the NWCR who at entry had lost at least 30 lbs (13.6 kg) and kept it off for at least one year. Data were collected in 1993-2010; analysis was conducted in 2012. Main outcome measures Weight loss (kilograms; percent weight loss from maximum weight). Results Mean weight loss was 31.3 kg (95% CI=30.8, 31.9) at baseline, 23.8 kg (95% CI=23.2, 24.4) at 5 years and 23.1±0.4 kg (95% CI=22.3, 23.9) at 10 years. More than 87% of participants were estimated to be still maintaining at least a 10% weight loss at Years 5 and 10. Larger initial weight losses and longer duration of maintenance were associated with better long-term outcomes. Decreases in leisure-time physical activity, dietary restraint, and frequency of self-weighing and increases in percentage of energy intake from fat and disinhibition were associated with greater weight regain. Conclusions The majority of weight lost by NWCR members is maintained over 10 years. Long-term weight-loss maintenance is possible and requires sustained behavior change. © 2014 American Journal of Preventive Medicine.