BACKGROUND: Inhaled corticosteroids are the agents of choice for treating persistent asthma. OBJECTIVE: To evaluate the long-term efficacy and safety of budesonide inhalation powder (Pulmicort Turbuhaler) in patients with mild to severe persistent asthma. METHODS: Patients (n=1133) received open-label budesonide (dose range, 100-800 microg b.i.d.) for 52 weeks following 2 weeks to 5 months of treatment in one of four double-blind, placebo-controlled studies. Patients, identified before the double-blind studies, included adults (n=249) not receiving corticosteroids, adults (n=384) and children (n=356) previously maintained on inhaled corticosteroids, and adults (n=144) previously maintained on oral corticosteroids. RESULTS: Mean forced expiratory volume in 1 sec was 68.2% of predicted normal (n=1133) at baseline (mean from two visits before randomization), 74.4% (n=1132) at the end of double-blind treatment, 81.3% (n=971) at week 52, and 80.1% (n=1125) at last observation (including patients who discontinued early). Sixty-four patients maintained on oral corticosteroids before double-blind treatment entered the open-label study off oral corticosteroids, 58 of whom (91%) remained oral corticosteroid-free throughout the study. There was no evidence of basal or cosyntropin-stimulated hypothalamic-pituitary-adrenal axis function suppression, and the most commonly occurring adverse events were respiratory infection, sinusitis, and pharyngitis. CONCLUSIONS: During this 52-week, open-label study, budesonide maintained the improved pulmonary function and decreased oral corticosteroid use observed during previous double-blind treatment and was well tolerated, supporting its long-term use in adults and children with mild to severe persistent asthma.