Inhaled budesonide has been demonstrated to be effective and safe when it is used in the prophylaxis of severe asthma in adults and school-age children but has not been studied in younger patients with asthma. Sixteen children, aged 3 1/2 to 7 years, with severe asthma, were treated with budesonide aerosol, 200 micrograms daily, via a spacer for 1 year in an open study. One month after starting budesonide therapy, a significant decrease in the number of days with asthmatic symptomatology, mean symptom scores, use of concomitant antiasthmatic medications, and increase in the peak expiratory flow rates were observed compared with the 1 month run-in period. This improvement was maintained throughout the year with budesonide therapy. During the study period, the height and weight of the children were not significantly deviated from the expected, and their bone age advanced normally. Adrenal function, as evaluated by fasting 8 AM blood cortisol levels and after adrenocorticotropic hormone stimulation, demonstrated no adverse effects with budesonide therapy. The suspectibility to severe infections was low, as evidenced by infrequent use of antibiotics. We conclude that a 12-month administration of inhaled budesonide to preschool-age children is safe and efficient and can be useful in the management of severe asthma in this young age group.