Background: Olfactory disorders are a common syndrome in the rhinology clinic. Olfactory event-related potential (OERP) has been considered as an important alternative method to evaluate olfactory function. The aim of this study was to find the consistency of OERP and the psychophysics olfactory test (T&T olfactometry assessment) in rhinosinusitis patients with or without nasal polyposis. Methods: Both the psychophysics olfactory test and the OERP were performed in all patients before functional endoscopic sinus surgery (FESS). Detailed information including demographic, comorbidity, subjective symptoms, CT, and endoscopic examination were recorded. Six months later, the T&T test and OERP were reexamined in patients with preoperative identified OERP. Results: Preoperative OERP was identified in 26 patients of the non polyp group and 12 patients of the polyp group. Good correlation existed between T&T scores and amplitude and latency of N1 and P2 in 26 nonpolyp patients (p < 0.05). No meaningful correlation was apparent in 12 polyp patients (p > 0.05). Significant correlation existed in 7 polyp patients with a free olfactory cleft (OC) according to CT (p < 0.05). The other 5 patients with partial OC obstruction were anosmic according to the psychophysics olfactory test; however, OERP was present. Six months later, T&T scores decreased significantly only in these five patients (p < 0.05). Significant correlation was obtained between postoperative T&T scores and OERP in both polyp and non polyp groups (p < 0.05). Conclusion: OERP can be used to investigate olfactory function of rhinosinusitis patients. Nasal polyp obstruction in specific parts of the OC might influence the consistency between the psychophysics olfactory test and OERP. (Am J Rhinol Allergy 24, 330-335, 2010; doi: 10.2500/ajra.2010.24.3517)