OBJECTIVES:To investigate what weight management interventions work for men, with which men, and under what circumstances. DESIGN:Realist synthesis of qualitative studies. DATA SOURCES:Sensitive searches of 11 electronic databases from 1990 to 2012 supplemented by grey literature searches. STUDY SELECTION:Studies published between 1990 and 2012 reporting qualitative research with obese men, or obese men in contrast to obese women and lifestyle or drug weight management were included. The studies included men aged 16 years or over, with no upper age limit, with a mean or median body mass index of 30 kg/m(2) in all settings. RESULTS:22 studies were identified, including 5 qualitative studies linked to randomised controlled trials of weight maintenance interventions and 8 qualitative studies linked to non-randomised intervention studies, and 9 relevant UK-based qualitative studies not linked to any intervention. Health concerns and the perception that certain programmes had 'worked' for other men were the key factors that motivated men to engage with weight management programmes. Barriers to engagement and adherence with programmes included: men not problematising their weight until labelled 'obese'; a lack of support for new food choices by friends and family, and reluctance to undertake extreme dieting. Retaining some autonomy over what is eaten; flexibility about treats and alcohol, and a focus on physical activity were attractive features of programmes. Group interventions, humour and social support facilitated attendance and adherence. Men were motivated to attend programmes in settings that were convenient, non-threatening and congruent with their masculine identities, but men were seldom involved in programme design. CONCLUSIONS:Men's perspectives and preferences within the wider context of family, work and pleasure should be sought when designing weight management services. Qualitative research is needed with men to inform all aspects of intervention design, including the setting, optimal recruitment processes and strategies to minimise attrition.