['Histological inflammation correlates with the degree of baseline olfactory dysfunction in patients with chronic rhinosinusitis (CRS); however, factors associated with improvement in olfactory status after endoscopic sinus surgery (ESS) remain elusive. Our purpose was to compare histopathological findings in CRS patients with olfactory loss and evaluate whether inflammatory markers can predict long-term olfactory improvement after ESS.', 'Adult (> or = 18 years) patients with CRS were prospectively enrolled after electing ESS due to failed medical management. Mucosal tissue specimens were collected at the time of surgery and underwent pathological review in a blinded fashion. Subjects completed the 40-item Smell Identification Test (SIT) preoperatively and at least 6 months postoperatively. Multivariate logistic regression was used to identify histological factors associated with postoperative improvement in SIT score.', 'The final cohort was comprised of 101 patients with a mean follow-up of 16.7 +/- 6.0 months. Mean mucosal eosinophil count was higher in patients with hyposmia and anosmia (p < 0.001). Patients with preoperative anosmia were more likely to have greater severity of basement membrane (BM) thickening compared with subjects with hyposmia or normosmia (p = 0.021). In patients with olfactory dysfunction, 54.7% reported olfactory improvement of at least 4 points on postoperative SIT scores. After controlling for nasal polyposis, histological variables were not associated with postoperative improvement in olfaction.'] Does ethmoid histopathology predict olfactory outcomes after endoscopic sinus surgery?