Inhaled corticosteroids (ICS) are considered the most effective asthma therapy, but concerns remain about side effects. The ideal ICS would have a larger therapeutic ratio than currently available agents, allowing doses to be increased but without greatly increasing the frequency or severity of adverse events. The ideal ICS would possess the following pharmacokinetic properties to maximize efficacy and minimize side effects: high pulmonary deposition, conversion to an active metabolite, high receptor potency, high pulmonary retention, low oral bioavailability, extensive metabolism, and rapid elimination. The new ICS ciclesonide has been shown to possess many of these characteristics. Ciclesonide has also been shown to improve lung function, to treat the underlying inflammation, to be effective as monotherapy in patients with persistent asthma, to have reduced side effects compared with other ICS, and to be easy to use with once-daily dosing. However, as with all new products, the advantages witnessed in clinical trials still have to be demonstrated to be beneficial long-term in general clinical use. ICS with an improved therapeutic index may have the potential to increase patient adherence, enhance the use of ICS monotherapy in the primary care setting, and increase the range of patients for whom ICS monotherapy would be appropriate.