BACKGROUND The aim of this study was to assess the possible relationship between sitting time and physical activity and the risk of occurrence of metabolic syndrome and its components. Analyses were conducted in the whole sample, and with stratification according to BMI. We have formulated a hypothesis that individuals with different BMIs have different responses to metabolic health modifiers such as physical activity and sitting time. MATERIAL AND METHODS Altogether, the data from 10 367 participants from urban and rural areas, aged 37-66 years were used in the study (7479 of whom were overweight or obese). The definition of metabolic syndrome devised by the IDF Joint Interim Statement criteria using an ethnic-specific cut-off point for waist circumference as the central obesity criterion was used. RESULTS In all analyzed BMI groups, longer sitting time was only associated with abdominal obesity (all p for trend <0.05). In participants declaring low physical activity levels, the risk of metabolic syndrome and abnormal triglycerides concentration was higher compared to those declaring high physical activity, regardless of BMI (all p for trend <0.05). In the group with overweight or obesity, low physical activity was associated with a higher risk of abdominal obesity (p for trend <0.05), increased glucose concentration (p for trend <0.05), and elevated blood pressure (p for trend <0.05). In participants with a normal BMI, these associations did not occur. CONCLUSIONS Our data suggest that physical activity helps preventive metabolic syndrome and its abnormal components, especially in participants who are overweight or obese.