This study was to evaluate the effectiveness of the first proactive Quitline service for smoking cessation in Korea and determine the predictors of successful smoking cessation. Smoking participants were voluntarily recruited from 18 community health centers. The participants were proactively counseled for smoking cessation via 7 sessions conducted for 30 days from November 1, 2005 to January 31, 2006. Of the 649 smoking participants, 522 completed 30 days at the end of the study and were included in the final analysis. The continuous abstinence rate at 30 days of follow-up was found to be 38.3% (200/522), in the intention-to-treat analysis. Compared with non-quitters, quitters were mostly male, smoked <20 cigarettes/day, had started smoking at the age of >or=20 yr, and were less dependent on nicotine. Based on the stepwise multiple logistic regression analysis, the significant predictors of successful smoking cessation were determined to be male sex, low cigarette consumption, and older age at smoking initiation. We investigated the short-term effectiveness of the Quitline service and determined the predictors of successful smoking cessation.