Background: Aspirin (acetylsalicylic acid [ASA]) hypersensitivity is frequent in patients with nasal polyps (NPs) and is called aspirin exacerbated respiratory disease, previously known as Samter's syndrome. However, studies evaluating the prevalence of ASA hypersensitivity in patients with NPs using the oral aspirin provocation test (APT) are quite limited. This study was designed to determine the prevalence of ASA hypersensitivity and factors associated with ASA hypersensitivity in patients with NPs. Methods: Sixty-eight patients with NPs with or without asthma were recruited. Extension of NPs was evaluated by endoscopic examination/paranasal CT. A 2-day, single-blind placebo-controlled APT was used to detect ASA hypersensitivity. Results: APT was performed in 53 (21 women/ 32 men) patients (mean age, 39.34 ± 1.76 years). APT resulted positive in 12 patients (22.6%) of whom 3 (25%) had no history of ASA hypersensitivity. Of the positive APTs, three were isolated rhinitis and nine had classic responses. APT was negative in 41 patients (77.4%) although three (7.3%) had a history of ASA hypersensitivity. History of ASA hypersensitivity and prolonged duration of NPs were associated with positive APT (p < 0.05). Advanced NP with multiple operations was also correlated with APT positivity but was not statistically significant. Presence of asthma was associated with age, female gender, NP duration, and ASA hypersensitivity history (p < 0.05), but not with smoking, atopy, NP extension, and positive APT. Conclusion: ASA hypersensitivity is quite common in patients with NP. Patients with extensive and long-term NP with multiple polyp operations require evaluation for the presence of ASA hypersensitivity in terms of chronic management and future risks of the disease. Copyright © 2011, OceanSide Publications, Inc., U.S.A.