A meta-analysis of the efficacy of cognitive behavioral therapy (CBT) in treating chronic fatigue included 15 effect sizes for between-group outcome comparisons. Across analyses, which included a total of 1371 participants, there was a significant difference, d = 0.48, in post-treatment fatigue between participants receiving CBT and those in control conditions. Results indicate that CBT for chronic fatigue syndrome tends to be moderately efficacious. Dropout rates in CBT varied from 0–42%, with a mean of 16%. In the five studies that reported the number of CBT clients who were no longer in the clinical range with regard to fatigue at the latest follow-up, the percentage varied from 33% to 73% of those assigned to CBT, with a mean of 50%. Moderator results suggest directions for future investigations.