Introduction: As elective surgical services recover from the COVID-19 pandemic a movement towards day-case surgery may reduce waiting lists. However, evidence is needed to show that day-case surgery is safe for endoscopic sinus surgery (ESS). The aim of this study was to investigate the safety of day-case ESS in England.Design: Secondary analysis of administrative data.Methods: We extracted data from the Hospital Episodes Statistics database for the 5 years from 1 April 2014 to 31 March 2019. Patients undergoing elective ESS procedures aged ≥17 years were included. Exclusion criteria included malignant neoplasm, complex systemic disease and trans-sphenoidal pituitary surgery. The primary outcome was readmission within 30 days post-discharge. Multilevel, multivariable logistic regression modelling was used to compare outcomes for those operated on as day-cases and those with an overnight stay after adjusting for demographic, frailty, comorbidity and procedural covariates.Results: Data were available for 49 223 patients operated on across 129 NHS hospital trusts. In trusts operating on more than 50 patients in the study period, rates of day-case surgery varied from 20.6% to 100%. Nationally, rates of day-case surgery increased from 64.0% in the financial year 2014/2015 to 78.7% in 2018/2019. Daycase patients had lower rates of 30-day emergency readmission (odds ratio 0.71, 95% confidence interval 0.62 to 0.81). Outcomes for patients operated on in trusts with ≥80% day-case rates compared with patients operated on in trusts with <50% rates of day-case surgery were similar.Conclusions: Our data support the view that ESS can safely be performed as daycase surgery in most cases, although it will not be suitable for all patients.