Severe fatigue following coronavirus disease 2019 (COVID-19) is prevalent and debilitating. In the ReCOVer study, the efficacy of cognitive-behavioral therapy (CBT) for severe fatigue following COVID-19 was investigated. This was a multicenter, 2-arm randomized controlled trial conducted in the Netherlands with patients being severely fatigued 3-12 months following COVID-19. Patients were recruited by physicians of 6 participating hospitals in the Netherlands, by healthcare providers, and by self-referral. Patients were assessed for eligibility from November 2020 to September 2021. Patients (n = 114) were randomly assigned (1:1) to CBT or care as usual (CAU). CBT, targeting perpetuating factors of fatigue, was provided for 17 weeks. The primary outcome was the overall mean difference between CBT and CAU on the fatigue severity subscale of the Checklist Individual Strength, directly post-CBT or CAU (T1), and after 6 months (T2). Secondary outcomes were differences in proportions of patients meeting criteria for severe and/or chronic fatigue, differences in physical and social functioning, somatic symptoms, and problems concentrating between CBT and CAU. For the CBT group, an uncontrolled T3 assessment was administered to measure the treatment effect 1 year after intervention completion. Patients who received CBT were significantly less severely fatigued across follow-up assessments (T1/T2) compared to patients receiving CAU (Cohen’s d effect size of 0.69). All secondary outcomes favored CBT. The uncontrolled long-term follow-up study (T3) revealed that favorable outcomes of CBT were maintained at least up to 1 year post-intervention. The dataset entails data of outcomes (see above), cognitive-behavioral factors, actigraphy, personal and demographic characteristics and COVID-19 related variables. See the protocol paper for an overview (Kuut et al., 2021).