Smoking cessation is the cornerstone of COPD management, but difficult to achieve in clinical practice. The effect of comorbidities on smoking cessation and risk factors for mortality were studied in a cohort of 739 COPD patients recruited in two Finnish University Hospitals. The diagnosis of COPD was done for the first time on average 5.5 years prior to the enrollment. Data from the medical records and followup questionnaires (years 0, 1, 2, and 4) have been analyzed. The patients' lung function varied greatly; mean FEV(1) 58% of predicted. A total of 60.2% of men and 55.6% of women had been able to quit smoking. Alcohol abuse (OR 2.1, 95% CI 1.4-3.3) and psychiatric conditions (OR 1.8, 95% CI 1.2-2.7) were strongly related to low success rates of quitting. Among current smokers high nicotine dependency was again explained by alcohol abuse and psychiatric conditions. Non-quitters were younger than quitters, but their mortality rates remained significantly higher even when the model was adjusted for impairment of lung functions and comorbidities. In conclusion, co-existing addiction and psychiatric diseases significantly decreased the success rates in smoking cessation and increased mortality among the patients.