Thirty-six individuals participated in a worksite weight-loss program in which the central component was a self-motivation program of biweekly payroll deductions refunded contingent on meeting self-selected weight-loss goals. Half were assigned to early treatment and the remainder to a delayed treatment control group. Nine additional individuals also enrolled at the time of delayed treatment and were included in descriptive analyses of factors associated with weight loss. Results showed low program attrition over 6 months (6%) and mean weight losses (12.3 lb) that are competitive with those obtained in clinical settings. Although not different at baseline, participants in the delayed treatment group lost more than twice as much weight as those in the early treatment condition. This difference was interpreted as either a strong seasonal effect or a critical mass effect related to the proportion of employees at the worksite participating in the program. We conclude that self-motivation programs for health behavior change using the payroll system as an organization framework offer a promising new methodology for promoting healthful behaviors in work settings.