OBJECTIVES: To evaluate the associated costs (from a 3rd payer perspective) due to the treatment of hospitalized Chronic Obstructive Pulmonary Disease (COPD) exacerbation.METHODS: Retrospective review of 246 clinical episodes of exacerbation in 4 tertiary hospitals (from June-1999 to December-2001), a 5th hospital data are under evaluation. The cost of the stay (hotel cost) used was €228,12/day (DRG 88 of one of the participating centers). The cost of the Diagnostic Tests was taken from the 2002 scale of the Physicians Medical College of Barcelona. Cost of the medication used: the MSP according to the cheapest prices published in the 2002 Pharmaceutical Official Book. RESULTS: (In brackets means per patient or episode). Total Days of Hospitalization: 1,911 (7.77), Total Cost of Hospitalization or Hotel Cost: €435,937.32 (1,772.10), Total Cost of Diagnosis Tests: 23,284.93€ (94.65), Total Cost of Oxygen-therapy and other treatments: €3,646.36 (14.82), Total Sum Cost of Hospital Pharmacological Treatment: €24,644.79 (100.18), Total Sum Cost of Continuing Therapy after discharge: €7,071.79 (28.75). The final Total Cost was €494,585.19, with an Average Cost per patient or episode of €2,010.51, and an Average Daily Cost per patient of €258.75. CONCLUSIONS: Total cost of COPD exacerbation is mainly determined by the hospital costs (88.1% of the final cost) and, secondarily, by the hospital pharmacological treatment cost (5.0%) and by the diagnosis tests cost (4.7%).