Technical Abstract: To determine whether a behavioral Internet treatment (BIT) program for weight management is a viable, cost-effective option compared with usual care (UC) in a diverse sample of overweight (average body mass index = 29 kg/m2), healthy adults (mean age = 34 years) serving in the US Air Force. Two-group parallel randomized controlled trial. Participants were randomly assigned into 2 groups: UC (n = 215) and UC plus BIT (n = 227). Baseline and 6-month assessments were included in the analyses. Primary outcome measures (changes in body weight, percent body fat, and waist circumference) and secondary outcome measures (Weight Efficacy Lifestyle [WEL] questionnaire) were included in an incremental cost-effectiveness analysis (ICEA) model. Costs were computed using the perspective of an agency wanting to replicate the intervention. Sensitivity analyses were performed to measure the robustness of models. Overall cost for BIT intervention was $11,178.40, or $49.24 per BIT participant. Total staff-time cost was $14.03 per BIT participant. Intervention cost was $25.92 per kilogram of weight loss and $28.96 per centimeter of waist-circumference loss. The cost was $37.88 for each additional point gained on the WEL subscale, where increasing scores indicate increased confidence in managing social pressures to eat. The BIT program is a cost-effective choice for weight management. It may cost more initially, but it results in long-term cost savings. Such cost-effective, Internet-based behavioral interventions for weight management could provide a valuable tool for preventive care aimed at improving individual and societal health.