Objective: The prevalence and associated health cost of asthma have been increasing in developed countries, and 70% of the overall disease cost is due to exacerbations. The primary objective of this study was to determine the hospital cost of an asthma exacerbation in Spain. The secondary objective was to determine what maintenance treatments patients were using to control asthma before the exacerbation and how the exacerbation was treated. The study formed part of a broader study (COAX II), with the same objectives in each of the 8 participating European countries., Patients and Methods: Prospective observational study that enrolled 126 patients with an asthma exacerbation treated in the usual way in 6 Spanish hospitals over a 3-month period (from January 1 to March 31, 2000)., Results: According to the criteria of the Global Initiative for Asthma, 33.3% of the exacerbations were mild, 38.9% moderate, 26.2% severe, and 1.6% were associated with risk of imminent respiratory arrest. Use of corticosteroids was widespread among patients with moderate and severe asthma, but only 68% of the patients with severe asthma used long-acting beta2 agonists. The mean cost was 1555.70 Euros (95% confidence interval [CI], 1237.60 Euros-1907.00 Euros), of which 93.8% (1460.60 Euros; 95% CI, 1152.50 Euros-1779.40 Euros) was due to direct costs, and 6.2% (95.10 Euros; 95% CI, 35.50 Euros-177.00 Euros) to indirect costs. Cost rose with increasing severity of the exacerbation--292.60 Euros for a mild exacerbation, 1230.50 Euros for a moderate exacerbation, and 3543.10 Euros for a severe exacerbation., Conclusions: The mean cost was 1555.70 Euros. The costs of moderate and severe exacerbations were 4 and 12 times that of a mild exacerbation, respectively. Long-acting beta2 agonists were less widely used than recommended by the guidelines for treatment of moderate and severe persistent asthma leading to asthma exacerbations.