The metabolic syndrome (MetS) is a clustering of individual cardiovascular disease risk factors, which doubles the risk of early mortality. The authors' aimed to determine the prevalence and population attributable risk (PAR%) of the MetS among men according to demographic, physical, and lifestyle risk factors. A cross-sectional study was conducted in 1195 men in the Florey Adelaide Male Ageing Study, a regionally representative cohort of Australian men aged 35 to 81 years conducted in 2002-2005 (response rate, 45.1%). Prevalent MetS was determined according to the Adult Treatment Panel III (ATPIII) and International Diabetes Federation (IDF) classifications; and an extensive list of demographic, physical (including muscle strength, body composition by dual-energy x-ray absorptiometry, sex hormones), and lifestyle factors was accounted for. Prevalence estimates were 37.7% and 41.8% for ATPIII and IDF classifications. Odds ratios for present MetS were determined using multiple-adjusted logistic regression. Odds for present ATPIII MetS decreased (in order of importance) for lower insulin and increased for lower muscle mass, lower strength, and 3+ medical conditions. Odds for present IDF MetS decreased for lower insulin and increased for lower muscle mass, strength, and sex hormone-binding globulin levels; older age; and being married. Significant PAR% due to lowest insulin, muscle mass, and strength quarters were -44%, 27%, and 17% for the ATPIII Met, and -48%, 31%, and 20% for the IDF MetS. A substantial proportion of MetS cases would have been theoretically prevented if prior exposure to low muscle mass and strength were eradicated (PAR% ranged from 14% to 24%). Findings indicate that insulin resistance is a central abnormality in the MetS and that muscle mass and strength are strong protective factors independent of insulin resistance and abdominal fat accumulation. If confirmed prospectively, increases in muscle mass and strength needed to prevent a substantial proportion of MetS cases would be achievable with a short-term strength training intervention.