Background: Patients with mild intermittent or mild persistent asthma represent 70% of asthma sufferers. Inhaled corticosteroids (ICSs) are the mainstay of treatment for persistent asthma, although many of the early clinical studies of these drugs included only patients with moderate to severe asthma.Objective: This article reviews the literature on the efficacy of budesonide in the treatment of mild persistent asthma, including newly diagnosed ICS-naive patients.Methods: Published data were identified by a MEDLINE search of the English-language literature from 1992 to 2002 using the terms budesonide plus efficacy or safety, both with and without the terms fluticasone or beclomethasone. An AstraZeneca reference database was also used to identify publications from the same period. Controlled, randomized studies that included patients with mild persistent asthma and early-treatment intervention were selected for inclusion.Results: Inhaled budesonide has been used for almost 20 years in the treatment and control of moderate to severe asthma. Studies involving patients with mild persistent asthma have demonstrated significant improvements in peak expiratory flow (PEF) rates (P < 0.01) and forced expiratory volume in I second (P < 0.016) values for adult, adolescent, and pediatric patients treated with budesonide compared with placebo. Budesonide therapy is effective when given once or twice daily via dry powder inhaler or nebulizer, even at a low starting dose (200 μg/d). No significant adverse events have been reported with budesonide within the dose range used to treat mild persistent asthma (200 to 400 μg/d). Significant improvements in PEF rates (P < 0.01) and significant reductions in the risk of exacerbations and the number of days with poorly controlled asthma have been reported for ICS-naive patients treated with budesonide compared with placebo (both P < 0.001). In the primary care setting, mild persistent asthma may be undertreated. Patients with mild persistent asthma benefit significantly from early treatment with budesonide (P < 0.05).Conclusions: Budesonide is effective and well tolerated in the treatment of mild persistent asthma in adults and children, including many patients whose primary care physicians do not think they require daily ICS treatment.