Purpose: The purpose of this study was to evaluate the effectiveness of a telephone support group program on spouses and adult child caregivers of frail older adults. Design and Methods: The Telephone Support Group (TSG) model is a multicomponent group program offered in 12 weekly, 90-minute group sessions. It includes emotion-focused and problem-focused coping strategies, education, and support. We recruited for this study 36 spouses and 61 adult children and randomly assigned them to TSG or to usual services. We assessed the participants before and after the completion of TSG or usual services. Results: The results indicated that, for adult child caregivers, TSG was more effective than usual services in reducing burden, depression, social support, and pressing problems, and increasing knowledge and use of community services. We found no significant differences for spouse caregivers. Implications: This is the first study to compare the effectiveness of TSG for adult child and spouse caregivers of frail older adults. TSG showed itself to be an effective means of delivering support to adult child caregivers of frail older adults but not to spouses. More research is needed about how to make TSG effective for spouse caregivers.