Objective: Chronic fatigue syndrome (CFS) symptoms have been shown to be exacerbated by stress and ameliorated by group-based psychosocial interventions such as cognitive behavioral stress management (CBSM). Still, patients may have difficulty attending face-to-face groups. This study compared the effects of a telephone-delivered (T-CBSM) vs a live (L-CBSM) group on perceived stress and symptomology in adults with CFS. Methods: Intervention data from 100 patients with CFS (mean age 50 years; 90% female) participating in T-CBSM (N = 56) or L-CBSM (N = 44) in previously conducted randomized clinical trials were obtained. Perceived Stress Scale (PSS) and the Centers for Disease Control and Prevention symptom checklist scores were compared with repeated measures analyses of variance in adjusted and unadjusted analyses. Results: Participants across groups showed no differences in most demographic and illness variables at study entry and had similar session attendance. Both conditions showed significant reductions in PSS scores, with L-CBSM showing a large effect (partial epsilon(2) = 0.16) and T-CBSM a medium effect (partial epsilon(2) = 0.095). For CFS symptom frequency and severity scores, L-CBSM reported large effect size improvements (partial epsilon(2) = 0.19-0.23), while T-CBSM showed no significant changes over time. Conclusions: Two different formats for delivering group-based CBSM live and telephone showed reductions in perceived stress among patients with CFS. However, only the live format was associated with physical symptom improvements, with specific effects on post-exertional malaise, chills, fever, and restful sleep. The added value of the live group format is discussed, along with implications for future technology-facilitated group interventions in this population. (C) 2016 Elsevier Inc. All rights reserved.