['Metabolic syndrome (MetS) develop by accumulation of excess central obesity occurring insulin resistance. In 2005, the Japanese Society of Internal Medicine, in collaboration with seven other Japanese societies defined the diagnostic criterion for Japan-specific MetS. Smoking also causes insulin resistance to develop. To clarify whether smoking is correlated with MetS and how long MetS remains after smoking cessation we undertook a retrospective study.', 'The subjects comprised of 22,892 Japanese who visited the Health-Care Center at Jikei University Hospital in Tokyo for medical check-ups. The participants completed a simple, self-administered questionnaire on their lifestyle including smoking information. MetS was diagnosed with the above criterion. The odds ratio (OR) with a 95% confidential interval (95%CI) of MetS was calculated using multiple logistic regression analysis adjusted by age and gender.', 'Compared with never smokers (n=9,434: 41%), the odds ratio (95% CI) of MetS onset for current smokers (n=7,634: 33%) and past smokers (n=5,824: 25%) were 1.20 (1.07-1.35) and 1.21 (1.08-1.37). In the current smokers, the odds ratio of MetS increased with the smoking number, and it significantly occurred by smoking > or = 20 cigarettes per day. After quitting, the longer cessation period is related to the lesser chance of developing of MetS. But, MetS remained for at least 10 years and over in the subjects who smoked 20 or more cigarettes per day, and for over 20 years in the subjects who smoked 40 cigarettes and more.'] Does risk of metabolic syndrome persist twenty years after the cessation of smoking?