The lifetime risk of acquiring HIV infection in many rural as well as urban areas of southern Africa is currently as high as two-in-three. For women, much of this risk still accrues rapidly at young ages despite high levels of knowledge about HIV/AIDS. Thus, programmes that are more participatory and address underlying structural and community-level factors appear to be essential. We use cross-sectional data from a large-scale, population-based survey in rural eastern Zimbabwe to describe the relationships between membership of different forms of community group and young women's chances of avoiding HIV. Our results show that participation in local community groups is often positively associated with successful avoidance of HIV, which, in turn, is positively associated with psychosocial determinants of safer behaviour. However, whether or not these relationships hold depends on a range of factors that include how well the group functions, the purpose of the group, and the education level of the individual participant. We identify factors that may influence the social capital value of community groups in relation to HIV prevention at the individual, group, and community levels. Young women with secondary education participate disproportionately in well-functioning community groups and are more likely to avoid HIV when they do participate. Longitudinal studies are needed: (i) to establish whether community group membership supports the development of safer lifestyles or merely has greater appeal to individuals already predisposed towards such lifestyles, and (ii) to pinpoint directions of causality between hypothesised mediating factors. In-depth research is needed on the specific qualities of community groups that enhance their contribution to HIV control. However, our findings suggest that promotion of and organisational development and training among community groups could well be an effective HIV control strategy.