OBJECTIVES: The aim of this study was to assess the cost-effectiveness of a class-based exercise program supplementing a home-based program when compared with a home-based program alone. In addition, we estimated the probability that the supplementary class program is cost-effective over a range of values of a decision maker's willingness to pay for an additional quality-adjusted life-year (QALY). METHODS: The resource use and effectiveness data were collected as part of the clinical trial detailed elsewhere. Unit costs were estimated from published sources. The net benefit approach to cost-effectiveness analysis is used to estimate the probability of the intervention being cost-effective. RESULTS: The addition of a supplementary class-based group results in an increase in QALYs and lower costs. For all plausible values of a decision maker's willingness to pay for a QALY, the supplementary class group is likely to be cost-effective. CONCLUSIONS: The addition of a class-based exercise program is likely to be cost-effective and, on current evidence, should be implemented.