BACKGROUND AND OBJECTIVE: Aspirin-intolerant asthma (AIA) is a distinct clinical syndrome characterized by aspirin sensitivity, asthma, and nasal polyposis (NP). The incidence of AIA in adult asthmatics is 8~20%, and the prevalence of AIA among adult asthmatics with NP and/or chronic rhinosinusitis further increases to 30~40%. However, the prevalence of subclinical AIA in patients with NP and/or chronic rhinosinusitis has rarely been investigated. METHOD: A total of 36 patients with NP and chronic rhinosinusitis who was scheduled for polypectomy were enrolled. All had no previous history of AIA. Lysine-aspirin bronchoprovocation tests were performed on all subjects before operation. Positive response was defined as a >15% fall in FEV1 from baseline. RESULT: Five of 36 patients (13.8%) showed positive responses to lysine-aspirin provocation tests (4 subject with NP+asthma and 1 with NP alone, P<0.05). There was a significant difference in the PC20 to methacholine between AIA+NP and NP+asthma groups (0.22+/-0.37 vs. 3.13+/-2.70 mg/mg, P<0.05), and peripheral blood eosinophil counts tended to increase from NP alone through NP+asthma to AIA+NP group (P<0.01). CONCLUSION: The prevalence of subclinical AIA in patients with NP and chronic rhinosinusitis was 13.8%, and AIA was especially more prevalent in the asthmatics with NP and chronic rhinosinusitis.