OBJECTIVE: To determine the health-care utilisation and associated costs for asthma and chronic obstructive pulmonary disease (COPD) in the Netherlands for the year 2000 and to estimate future costs by means of projections. DESIGN: Descriptive and explorative. METHOD: The costs were based on data regarding resource use in 2000 obtained from representative national registries and surveys. The costs were specified by gender and age category and for COPD also by severity. Three projections for the costs of asthma and COPD were made by means of prevalence projections: first assuming constant resource use and constant prices, second assuming asthma- and COPD-specific trends in the costs for hospital care (asthma, -4.7% and COPD, -4.1% per year) and medication (+4.9% per year), and third by adding general trends for the remaining types of care. RESULTS: Total costs for the year 2000 for asthma (452,000 patients) and COPD (306,000 patients) were estimated to be 141 and 280 million Euros, amounting to 313 en 915 Euros per patient or 9 and 18 Euros per inhabitant, respectively. Projections of total prevalence for the year 2025 varied between 478,000 and 568,000 patients for asthma and between 479,000 and 494,000 patients for COPD. Assuming constant resource use and prices, the costs in 2025 were projected to increase to amounts between 167 and 181 million Euros for asthma and 443 and 495 million Euros for COPD. Projections including the estimated trends in costs for hospital care, medication and the costs for other types of care predicted a sharper increase. CONCLUSION: Costs for asthma and COPD together (421 million Euros) amounted to 1.3% of the total Dutch health-care budget in 2000. Almost 70% of these costs were for COPD. Projections for 2025 showed that the costs for COPD will increase more than the costs for asthma.