BACKGROUND: Social and lifestyle influences on age-related changes in body morphology are complex because lifestyle and physiological response to social stress can affect body fat differently. OBJECTIVE: In this study, we examined the associations of socioeconomic status (SES) and lifestyle factors with BMI and waist circumference (WC) in middle-aged and elderly European men. DESIGN AND SETTING: A cross-sectional study of 3319 men aged 40-79 years recruited from eight European centres. OUTCOMES: We estimated relative risk ratios (RRRs) of overweight/obesity associated with unfavourable SES and lifestyles. RESULTS: The prevalence of BMI ≥ 30 kg/m(2) or WC ≥ 102 cm rose linearly with age, except in the eighth decade when high BMI, but not high WC, declined. Among men aged 40-59 years, compared with non-smokers or most active men, centre and BMI-adjusted RRRs for having a WC between 94 and 101.9 cm increased by 1.6-fold in current smokers, 2.7-fold in least active men and maximal at 2.8-fold in least active men who smoked. Similar patterns but greater RRRs were observed for men with WC ≥ 102 cm, notably 8.4-fold greater in least active men who smoked. Compared with men in employment, those who were not in employment had increased risk of having a high WC by 1.4-fold in the 40-65 years group and by 1.3-fold in the 40-75 years group. These relationships were weaker among elderly men. CONCLUSION: Unfavourable SES and lifestyles associate with increased risk of obesity, especially in middle-aged men. The combination of inactivity and smoking was the strongest predictor of high WC, providing a focus for health promotion and prevention at an early age.