Asthma represents a growing public health problem and the cost of asthma has been rising in many countries. The aim of this study was to estimate the direct and indirect cost of asthma among adult patients in Italy, and to assess the relationship between healthcare resource use and asthma severity according to the Global Initiative for Asthma (GINA) classification system.A multicentre cross-sectional study was conducted in 16 Italian hospital-based specialised asthma clinics. Data collection was based on self-administered questionnaires and took place during the period May 1-November 30, 1999, and 500 consecutive patients with asthma, aged 18-55 yrs, were enrolled during regularly scheduled visits. Direct costs (drugs, physician visits, emergency service use and hospitalisation), indirect costs (loss of paid workdays) and total costs were determined in euros (J) for 1999.Patients with more severe disease, as classified by the GINA guideline, exhibited more night-time and daytime symptoms and were more limited in performing normal daily activities. The mean total cost of asthma per patient per year was estimated to be J1,260; drug costs accounted for 16%, physician costs 12%, emergency service and hospitalisation costs 20% and indirect costs 52% of the mean cost. Stratified by severity, the total annual cost per patient amounted to J720, J1,046, J1,535 and J3,328 for patients with intermittent, mild persistent, moderate persistent and severe persistent asthma, respectively.Asthma severity, as determined by the Global Initiative for Asthma classification, is significantly associated with symptoms, limitations in normal daily activities, asthmarelated medical resource utilisation and both direct and indirect costs. Asthma control is not only a clinical but also an economic imperative.