Fibromyalgia (FM) is associated with significant economic costs. Given the limited availability of effective and accessible treatments, it is crucial to develop and assess the cost-effectiveness of new interventions. This study aimed to evaluate the cost-effectiveness of online exposure therapy (EXP-CBT) versus online traditional CBT (TCBT) for FM. We analyzed health economic data from a randomized controlled trial in which 274 participants with FM were assigned to either EXP-CBT or T-CBT. The time horizon was 15 months, and treatment effectiveness relative to costs was evaluated from both a societal perspective (direct and indirect costs) and a health care perspective (direct medical costs only). Bootstrapped net benefit regression analyses were conducted to compare cost and effect differences between EXP-CBT and T-CBT under various willingness-to-pay scenarios. The results showed that the incremental cost-effectiveness ratio was -1477/0.09 = -$16,884 from the societal perspective, indicating that EXP-CBT was cost-effective. Each additional successfully treated case (treatment responder) in EXP-CBT compared to T-CBT was associated with lower costs and there was a 69% probability of EXP-CBT being cost-effective even at a willingness-to-pay threshold of $0. The cost-utility analysis resulted in an estimate of -1477/0.05 = -$28,763, also here with an 69% probability of EXP-CBT being cost-effective at a willingness-to-pay threshold of $0. There were no significant differences in total costs or effectiveness between EXP-CBT and T-CBT. In conclusion, online exposure therapy may be a cost-effective alternative to online traditional CBT, but there appears to be no marked cost- or effect differences between the two treatments. Perspective: This article presents a cost-effectiveness evaluation of online exposure therapy compared to online traditional CBT for fibromyalgia. Results indicate that online exposure therapy may be cost-effective compared to online traditional CBT. However, as there were no marked cost- or effect differences between the treatments, results should be interpreted with caution.