BACKGROUND:Data on the effectiveness of employer-sponsored financial incentives for employee weight loss are limited.OBJECTIVE:To test the effectiveness of 2 financial incentive designs for promoting weight loss among obese employees.DESIGN:Randomized, controlled trial. (ClinicalTrials.gov: NCT01208350)SETTING:Children's Hospital of Philadelphia.PARTICIPANTS:105 employees with a body mass index between 30 and 40 kg/m2.INTERVENTION:24 weeks of monthly weigh-ins (control group; n = 35); individual incentive, designed as $100 per person per month for meeting or exceeding weight-loss goals (n = 35); and group incentive, designed as $500 per month split among participants within groups of 5 who met or exceeded weight-loss goals (n = 35).MEASUREMENTS:Weight loss after 24 weeks (primary outcome) and 36 weeks and changes in behavioral mediators of weight loss (secondary outcomes).RESULTS:Group-incentive participants lost more weight than control participants (mean between-group difference, 4.4 kg [95% CI, 2.0 to 6.7 kg]; P < 0.001) and individual-incentive participants (mean between-group difference, 3.2 kg [CI, 0.9 to 5.5 kg]; P = 0.008). Twelve weeks after incentives ended and after adjustment for 3-group comparisons, group-incentive participants maintained greater weight loss than control group participants (mean between-group difference, 2.9 kg [CI, 0.5 to 5.3 kg]; P = 0.016) but not greater than individual-incentive participants (mean between-group difference, 2.7 kg [CI, 0.4 to 5.0 kg]; P = 0.024).LIMITATION:Single employer and short follow-up.CONCLUSION:A group-based financial incentive was more effective than an individual incentive and monthly weigh-ins at promoting weight loss among obese employees at 24 weeks.