Since idiopathic chronic eosinophilic pneumonia (ICEP) and asthma are frequently associated, their possible reciprocal influence on clinical presentation and evolution were investigated. The clinical and follow-up features of 53 cases of ICEP, of which 41 (77%) had asthma, were reviewed retrospectively. Asthma preceded the diagnosis of ICEP in 26 patients, was contemporaneous in eight patients, and developed 17+/-12 months after ICEP in seven patients. Presentation of ICEP was similar in asthmatics and nonasthmatics with the exception of a higher level of total immunoglobulin E in the former group. Patients with asthma at the time of diagnosis of ICEP were more likely to remain free of relapse of ICEP (56 versus 23%) and had a lower number of relapses per year of follow-up (median 0 versus 0.24). Moreover, they were treated more frequently with long-term inhaled corticosteroids (88 versus 31%) at last follow-up. Asthma got worse after the diagnosis of ICEP and frequently required long-term oral corticosteroids. To conclude, among patients with idiopathic chronic eosinophilic pneumonia asthmatics have a lower frequency of relapse than nonasthmatics, possibly because of a higher use of inhaled corticosteroids. The occurrence of idiopathic chronic eosinophilic pneumonia in asthmatics is often associated with the development of severe asthma.