BACKGROUND: Eosinophilic bronchitis (EB) presents as a chronic cough and sputum eosinophilia without airflow limitation and bronchial hyperreactivity. The long-term clinical courses remain unknown. OBJECTIVE AND METHOD: The aim of this study was to evaluate how frequently EB recurs and whether it develops into chronic airway obstruction. Cough severity, FEV1, PC20 methacholine and sputum eosinophil percentages were serially measured in 36 subjects for up to 48 months. RESULT: Five subjects developed recurrent episodes of EB (RG) between 4 to 6 months after the first episode of EB. Asthma developed in the 9th month of the study in one of these subjects and a progressive FEV1 reduction exceeding 20% was observed in two. Nineteen subjects had no recurrence of EB (NRG). However, sputum eosinophilia recurred between 4 and 24 months in 10 subjects of the NRG, though this was without cough or FEV1 reduction. The follow-up eosinophil percentages were significantly higher in the RG than NRG group with recurrent sputum eosinophilia. CONCLUSION: About 14% of EB cases experience repeated episodes of EB and in about 30%, the EB recurs as asymptomatic sputum eosinophilia. Moreover, the extent of sputum eosinophilia was found to be associated with the recurrence of eosinophilic bronchitis, which leads to an airflow rate deterioration. These results suggest that repeated episode of EB is a risk factor for the development of asthma or chronic airway obstruction.