OBJECTIVE: To evaluate the association between physical activity, sleeping hours, alcohol intake and smoking and metabolic syndrome. METHODS: Social, demographic, personal and family medical histories and behavioral characteristics were collected as self-reported for 2164 participants (1332 women; 832 men), aged 18-92 years old, randomly selected during 1999-2003, among residents in Porto, Portugal, evaluated in the Department of Epidemiology of Porto Medical School. Metabolic syndrome was defined according to the NCEP-ATPIII. Associations between metabolic syndrome and lifestyles factors were computed as odds ratios (OR) and 95% confidence intervals (95% CI). RESULTS: After adjustment, higher total physical activity (OR=0.63 95% CI%: 0.43, 0.94--females; OR=0.55 95% CI: 0.33, 0.91--males) and work activity levels in females (OR=0.55; 95% CI: 0.33, 0.91) were significantly associated with lower prevalence of the metabolic syndrome. More sleeping hours were positively associated with metabolic syndrome (OR=1.25; 95% CI: 1.13, 1.38--females; OR=1.19; 95% CI: 1.04, 1.36--males). Regarding smoking, the only statistically significant association was found in women that smoked less than 10 cigarettes per day (OR=0.32 95% CI: 0.11, 0.92). No statistically significant association was found between ethanol intake and metabolic syndrome. CONCLUSIONS: An association between decreased physical activity, increased sleeping hours and metabolic syndrome was found. No association was found between cigarette smoking, alcohol intake and the metabolic syndrome.