Research has shown that cancer patients in general benefit from support group participation. However, few patients attend such groups. This study investigated differences between participants of a community cancer support group and a random selection of non-participants from the Cancer Registry. Data were collected through mail survey, and included variables identified through past research and variables derived from Leventhal's self-regulatory model of illness representations and the theory of planned behaviour. Sixty-three support group participants and 44 comparison sample respondents were recruited. Support group participants were more likely to be female, without a partner, younger, and to have more education and formal support than non-participants. They held more favourable views of support groups, believed that significant others were favourable towards participation, and perceived less difficulty in joining a group. They furthermore used more active, adaptive coping strategies and felt more control over their cancer, but were more distressed and anxious. Non-participants reported more support from a special person. A multivariate logistic regression analysis showed only psychosocial variables to be independent predictors of participation. As psychological variables are amenable to change, increase of appropriate support group participation should be possible, for instance by addressing patients' beliefs about support groups. Copyright © 2005 John Wiley & Sons, Ltd.