ObjectiveTo evaluate the effectiveness and safety of a Hasner's valve incision performed under endoscopic intranasal surgery for the management of congenital nasolacrimal duct obstruction.MethodsThis retrospective study comprised 484 patients with congenital nasolacrimal duct obstruction who underwent incision of Hasner's valve under endoscopic intranasal surgery between April 2000 and October 2016. The primary endpoint was the procedure's functional success rate. The secondary endpoints were Hasner's valve and inferior turbinate anatomical findings, demographic data, complication rate and surgical duration.ResultsIn patients with no medical history of nasolacrimal duct probing, 91 per cent had a successful result, 5 per cent had a partially successful result, 3.9 per cent showed no change and 0.1 per cent had a worse result following the procedure. Concerning the secondary endpoints, outcomes were more frequently successful in children younger than three years. Only one patient had a post-operative infection. All patients underwent general anaesthesia; no complications related to general anaesthesia were observed. Mean surgical duration was 13.1 ± 5.7 minutes.ConclusionIncising Hasner's valve after medially displacing the inferior turbinate under nasal endoscopy seems to be an adequate primary surgical treatment for congenital nasolacrimal duct obstruction.