Asthma and COPD are often considered mutually exclusive diseases, mainly because of the inclusion of only typical cases of asthma or COPD in therapeutic clinical trials. However, clinicians are unable to distinguish between both conditions in a substantial number of patients, a situation that may be called the "asthma-COPD overlap syndrome". It is important to recognize this entity, as patients suffering from an asthma-COPD overlap syndrome are more symptomatic, have a poorer quality of life and suffer more exacerbations than patients with asthma or COPD alone. In the absence of studies specifically designed to assess the treatment modalities for these patients, it appears wise to prescribe inhaled corticosteroids early in the course of the disease, considering their established efficacy in asthma.