We studied the complex relationship between nasal polyposis and ASA (acetylsalicylic acid) intolerance in 154 patients with nasal polyps. The clinical histories of all patients were reviewed, and diagnostic tests for immune or allergic causes and the responsiveness of patients to challenges with ASA-substitutive drugs were analyzed. A third of our patients tested were found to have positive personal histories of atopy and 35% showed ASA intolerance. Although 40% had bronchial asthma, only 16.8% of all patients had positive tests for allergy. We were unable to find a specific mechanism to explain the relationship between nasal polyposis and ASA intolerance and further investigations are still required.