Support groups for adults affected by cancer are widely offered by local community and national agencies in North America. This type of psychosocial intervention is defined in terms of its structure and functions, and its theoretical underpinnings and models of practice are described. Forty-four empirical studies of professionally led cancer support groups are summarized and critically reviewed. These studies include 32 outcome evaluations of randomized controlled trials, two process evaluations, and 10 consumer satisfaction studies. The findings reveal high levels of consumer satisfaction, and the outcome evaluations substantiate the morale and other quality of life benefits short of prolonging life. Discussion centers on priorities for future research and practice.