Purpose The study investigated the efficacy and cost-effectiveness of a cognitive-behavioral weight management program, complemented by an interactive Web site and brief telephone/e-mail coaching. Methods In 2006–2007, 1755 overweight, non-active-duty TRICARE beneficiaries were randomized to one of three conditions with increasing intervention intensity: written materials and basic Web access (RCT1), plus an interactive Web site (RCT2), plus brief telephone/e-mail coaching support (RCT3). The study assessed changes in weight, blood pressure, and physical activity from baseline to 6, 12, and 15–18 months. (Study retention was 31% at 12 months.) Average and incremental cost-effectiveness and cost-offset analyses were conducted. Results Participants experienced significant weight loss (− 4.0%, − 4.0%, and − 5.3%, respectively, in each RCT group after 12 months and − 3.5%, − 3.8%, and − 5.1%, respectively, after 15 to 18 months), increased physical activity, and decreased blood pressure. Cost-effectiveness ratios were $900 to $1100/quality-adjusted life year (QALY) for RCT1 and RCT2 and $1900/QALY for RCT3. The cost recovery period to the government was 3 years for RCTs 1 and 2 and 6 years for RCT3. Conclusion A relatively inexpensive cognitive-behavioral weight management intervention improved patient outcomes. Extrapolation of savings for the entire TRICARE population would significantly reduce direct medical costs.