BACKGROUND: The relationship between smoking, lifestyle, and weight, body mass index (BMI) and waist-to-hip ratio (WH ratio) is complex, and not fully understood. METHODS: In total, 6784 subjects (2408 daily smokers) were included in a population-based study (the Inter99 study) in Denmark. Weight, height, and waist and hip circumference were measured. Self-reported tobacco consumption and lifestyle variables (dietary quality, energy intake, physical activity in leisure time and alcohol consumption) were registered. RESULTS: Daily smokers had a significantly lower BMI and significantly higher WH ratio than never smokers (P<0.001). Unhealthy lifestyle increased with increasing tobacco consumption (P<0.001 for all variables). Both BMI and WH ratio increased with increasing tobacco consumption. The association between increasing WH ratio and increasing tobacco consumption was largely explained by sociodemographic factors, rather than lifestyle factors. However, neither sociodemographic nor lifestyle factors could fully explain the increased BMI associated with heavier smoking. CONCLUSIONS: Sociodemographic and lifestyle factors could not fully explain why BMI increased with increasing daily tobacco consumption, but these factors did largely explain the increasing WH ratio. The relationship between BMI and tobacco consumption is complex, and the public needs to be informed that smoking is not a 'diet'.