Background: Endoscopic sinus surgery (ESS) is often recommended for symptomatic patients with recurrent acute or chronic rhinosinusitis who have failed conservative treatment. Postoperative care has been felt to be critical for both maintaining the surgical patency of the operated sinuses and improving patient symptoms. Debridement of the sinonasal cavities is one such postoperative care measure that has frequently been studied in the literature, often with conflicting conclusions. Objectives: To assess the effects of postoperative sinonasal debridement versus no debridement following endoscopic sinus surgery. Search methods: The Cochrane ENT Information Specialist searched the ENT Trials Register; Central Register of Controlled Trials (CENTRAL, via the Cochrane Register of Studies); PubMed; EMBASE; Web of Science; ClinicalTrials.gov; ICTRP and additional sources for published and unpublished trials. The date of the search was 21 May 2018. Selection criteria: Randomised controlled trials comparing postoperative nasal debridement versus no debridement in adult patients with recurrent acute or chronic rhinosinusitis undergoing endoscopic sinus surgery. We included studies in which the patients acted as self-controls (i.e. one side of the nose underwent debridement and the other side did not) only for the secondary endoscopy outcomes. Data collection and analysis: We used the standard methodological procedures expected by Cochrane. Our primary outcome measures were: health-related quality of life, disease severity (patient-reported symptom scores) and significant adverse effects (bleeding requiring intervention, severe pain, iatrogenic injury). Secondary outcomes were: postoperative endoscopic appearance of the sinonasal surgical cavities (endoscopic scores), recorded use of postoperative medical treatment and rate of revision surgery. We used GRADE to assess the quality of the evidence for each outcome; this is indicated in italics. Main results: We included four studies (152 participants), with a follow-up duration ranging from three months to 12 months. In two studies patients acted as self-controls, i.e. one side of the nose underwent debridement and the other side did not ('split-nose' studies). The risk of bias in all studies was high, mostly due to the inability to blind the patients to the debridement procedure. Primary outcomes Disease-specific health-related quality of life scores Only one study (58 participants) provided data for disease-specific health-related quality of life. At six months follow-up, lower disease-specific health-related quality of life scores, measured using the Sino-Nasal Outcome Test-22 (SNOT-22, range 0 to 110), were noted in the debridement group but the difference was not statistically significant (9.7 in the debridement group versus 10.3 in the control group, P = 0.47) (low-quality evidence). Disease severity (patient-reported symptom score) Only one study (60 participants) provided data for disease severity measured by visual analogue scale (VAS) score. No significant differences in total symptom score were observed between groups postoperatively (low-quality evidence). Significant adverse effects Significant adverse effects related to the debridement procedure were not reported in any of the included studies, however it is not clear whether data regarding adverse effects were not collected or if none were indeed observed in any of the included studies. Secondary outcomes All four studies assessed thepostoperative endoscopic appearance of the sinonasal cavities using the Lund-Kennedy score (range 0 to 10). A pooled analysis of endoscopic scores in the two non 'split-nose' studies revealed better endoscopic scores in the debridement group, however this was not a statistically significant difference (mean difference -0.31, 95% confidence interval (CI) -1.35 to 0.72; I2 = 0%; two studies; 118 participants) (low-quality evidence). A sub-analysis of the adhesion formation component of the endoscopic score was available for all four studies and revealed a significantly lower adhesion rate in the debridement group (risk ratio 0.43, 95% CI 0.28 to 0.68; I2 = 29%; four studies; 152 participants). Analysis of the number needed to treat to benefit revealed that for every three patients undergoing debridement, the endoscopic score would be decreased by one point in one patient. For every five patients undergoing debridement adhesion formation would be prevented in one patient. Use of postoperative medical treatment was reported in all studies, all of which recommended nasal douching. Steroids (systemic or nasal) were administered in two studies. However, the data were very limited and heterogeneous, therefore we could not analyse the impact of concomitant postoperative medical treatment. The rate of revision surgery was not reported in any of the included studies, however it is not clear whether these data were not recorded or if there were no revision surgeries in any of the included studies. Authors' conclusions: We are uncertain about the effects of postoperative sinonasal debridement due to high risk of bias in the included studies and the low quality of the evidence. Sinonasal debridement may make little or no difference to disease-specific health-related quality of life or disease severity. Low-quality evidence suggests that postoperative debridement is associated with a significantly lower risk of adhesions at three months follow-up. Whether this has any impact on longer-term outcomes is unknown.