Chronic obstructive pulmonary disease (COPD) is one of the leading causes of morbidity and mortality worldwide. In Finland, the current prevalence of COPD is unknown. This population-based study aimed to assess the prevalence of COPD in Finland in adults 21-70 years of age by using internationally accepted criteria for COPD, and to evaluate risk factors for COPD. A random sample (n = 959) of questionnaire responders was invited to participate in a clinical study, which included a structured interview, skin-prick tests, and spirometry. Complete data were received from 683 subjects. According to the criteria of the British Thoracic Society and the Global Initiative for Chronic Obstructive Lung Disease, the prevalence of COPD was 5.4% and 9.4% respectively. The risk of COPD increased significantly with age, amount of smoking, and family history of obstructive airways disease, but not with skin-prick positive allergy, recreational skiing, or outdoor work. The smoking-adjusted risk of clinically relevant COPD did not differ significantly between men and women. Among subjects with a smoking history of more than 40 pack-years, the prevalence of COPD was over 50%. Early start age of smoking was a strong risk factor.