To examine the association between cigarette smoking and the risk of the metabolic syndrome (MS), 3,649 Japanese male office workers aged 35-59 yr who did not have a history of cardiovascular disease were enrolled in this study. 2,994 men without the MS at entry were followed up over a 7-yr period. A modified National Cholesterol Education Program definition with body mass index instead of waist circumference was used for the MS. With adjustment for age, family history of diabetes, alcohol intake, and regular physical activity, the odds ratios of the MS were 1.0 (referent), 1.30 (95% confidence interval (CI), 1.00-1.68), 1.07 (95% CI, 0.82-1.39), 1.17 (95% CI, 0.88-1.56), and 1.66 (95% CI, 1.24-2.20) for never smokers, ex-smokers, and those who smoked 1-20 cigarettes/d, 21-30 cigarettes/d, and ≥31 cigarettes/d, respectively (P for trend for current smokers only =0.006). As for the risk of developing the MS, the respective multivariate-adjusted hazard ratios of developing the MS were 1.0 (referent), 1.43 (95% CI, 1.14-1.79), 1.14 (95% CI, 0.91-1.44), 1.45 (95% CI, 1.14-1.84), and 1.59 (95% CI, 1.24-2.05) (P for trend for current smokers only =0.001). Among men without the MS at entry, body weight gain over 7 yr, compared with never smokers, was significantly higher in smokers who quit smoking. It is important for the prevention of the MS not only to quit smoking but also to prevent weight gain after smoking cessation.