This paper describes a population-based study of health care resource use of patients with chronic obstructive pulmonary disease (COPD) compared to non-COPD controls. Through a screening of the Danish Patient Registry for patients admitted with COPD diagnoses for a 5-year period, 1998-2002, 66,000 individuals with COPD still alive at the beginning of 2002 were identified. Their use of health care resources in 2002 were compared with equivalent data, stratified for age, sex and mortality rates, for a control population without COPD based on data for the 300,000 remaining patients on the Danish Patient Registry in 2002. Results indicated that the gross cost of treating patients with COPD in the Danish somatic hospital and primary health care sector corresponded to 10% of the total cost of treating patients of 40 years or more. The net cost for COPD patients was 1.9 billion DKK (256 million euro), 6% of the total annual costs of treating the population of 40 years or more. The gross cost related to any disease and the net cost reflected the resource use which could be attributed to COPD and its related diagnoses. The incidence of inpatient hospital admissions was almost four times higher in the COPD population than in the control group. COPD patients contacted their general practitioner 12 times more per year than non-COPD controls, but for specialist and paramedic treatment in the primary care sector there was no significant difference between COPD patients and non-COPD controls. Only one third of the COPD costs were due to treatment of COPD as the primary diagnosis. The remaining two-thirds of the COPD-related costs were mainly due to admissions for other diseases such as cardio-vascular diseases, other respiratory diseases, and cancer.