Background: The effectiveness of worksite interventions to reduce smoking is debatable. Objectives: Acomprehensive smoking cessation intervention was implemented in a community of more than 17,000 employees at three different health care companies. The primary endpoint was abstinence at 24 months (self-reported and confirmed by exhaled carbon monoxide ≤6 parts per million). Predictors of long-term abstinence were analysed by multivariable regression analysis. Methods: The study was designed as an investigator-initiated and investigator-driven, open, multicentre, cohort study; 887 smokerswere enrolled in the programme. The intervention included intensive individual counselling as well as nicotine replacement and/or bupropion according to individual preferences. Re-interventions for relapse were offered during the 24-month follow-up. Results: The abstinence rate was 37% at 24 months and did not differ among the various medication groups (p > 0.05 for all). Predictors of successful cessation were higher age (odds ratio, OR 1.47, 95% confidence interval, CI 1.08-2.00, p < 0.01), breathlessness on exertion (OR 2.26, 95% CI 1.1-4.9, p = 0.03), and a higher educational level (OR 1.81, 95% CI 1.06-3.09, p = 0.03). Higher Fagerström (OR 0.76, 95% CI 0.59-0.97, p < 0.01) and craving scores (OR 0.75, 95% CI 0.63-0.89, p < 0.01), chronic sputum production (OR 0.52, 95% CI 0.31-0.87, p = 0.01) and use of antidepressants (OR 0.54, 95% CI 0.32-0.91, p = 0.02) were associated with ongoing smoking. Conclusion: Acomprehensive smoking cessation intervention at the workplace achieves high, stable, long-term abstinence rates. Elderly, well-educated employees with breathlessness on exertion have higher odds of quitting smoking. In contrast, those with high physical dependency and more intense craving, and those reporting use of antidepressant medication or sputum production have poorer chances to quit.