Qualitative research may be able to provide an answer as to why adults and children do or do not participate in sport and physical activity. This paper systematically examines published and unpublished qualitative research studies of UK children's and adults' reasons for participation and non-participation in sport and physical activity. The review covers peer reviewed and gray literature from 1990 to 2004. Papers were entered into review if they: aimed to explore the participants' experiences of sport and physical activity and reasons for participation or non-participation in sport and physical activity, collected information on participants who lived in the United Kingdom and presented data collected using qualitative methods. From greater than 1200 papers identified in the initial search, 24 papers met all inclusion criteria. The majority of these reported research with young people based in community settings. Weight management, social interaction and enjoyment were common reasons for participation in sport and physical activity. Concerns about maintaining a slim body shape motivated participation among young girls. Older people identified the importance of sport and physical activity in staving off the effects of aging and providing a social support network. Challenges to identity such as having to show others an unfit body, lacking confidence and competence in core skills or appearing overly masculine were barriers to participation. (Contains 2 tables.)