This study has comparatively analyzed the primary success factors in smoking cessation among new enrollees and re-enrollees of a smoking cessation clinic in order to find out how to efficiently operate smoking cessation clinics at public health centers. The study was conducted with 262,837 smokers aged 19 or over who were provided with smoking cessation services for more than 6 months after being registered with the smoking cessation clinic at public health centers(250 clinics nationwide) from July 16, 2006 to July 15, 2007. After dividing smokers into re-enrollees and new enrollees of the smoking cessation clinic, the success rate of and success factors for smoking cessation over 6 months have been investigated. The success factors in smoking cessation have been compared between new enrollees and re-enrollees of smoking cessation clinics. The results can be summarized as follows: First, the success rate of smoking cessation for 6 months at smoking cessation clinics of public health centers was higher in new enrollees (46.3%) than in re-enrollees (41.1%). Second, the common factors that had an influence on the success of smoking cessation of both new enrollees and re-enrollees of the smoking cessation clinic included age, social security, service, frequency of counseling, number of cigarettes per day, and alcoholic problems. Third, compared to new enrollees, re-enrollees had a higher success rate of smoking cessation as they got older. In terms of the success rate of health insurance, on the contrary, new enrollees were better than re-enrollees. Fourth, the study showed a higher success rate in smoking cessation in both new and re-enrollees if they had no alcoholic problems. In particular, a higher success rate was observed in re-enrollees when there were no alcoholic problems. To efficiently operate smoking cessation clinics at public health centers, this study confirmed that counseling should be tailored depending on the types of enrollees in the program.