To report a patient with transient recurrence of lacrimal pressure regurgitation following a successful conventional external dacryocystorhinostomy.A 22-year-old female, who had undergone conventional external dacryocystorhinostomy, presented 3 days later with a recurrence of pressure regurgitation. The patient's symptoms disappeared spontaneously 7 days later. Serial naso-endoscopic examination was used to find the cause.Endoscopic examination showed an oedematous posterior nasal mucosal remnant obstructing the lacrimal drainage pathway. On account of its peculiar location, shape and movements, and the surgically induced tissue oedema, this mucosal remnant misdirected the fluid coming through the canalicular system away from the nasal cavity into the lacrimal pocket. Ten days later, due to healing fibrosis, this flap adhered permanently to the lateral nasal wall and the patient's symptoms disappeared spontaneously.Nasal endoscopy is a simple, quick and convenient technique for diagnosing the cause of obstruction in the lacrimal drainage system. The surgeon should aim for large anterior lacrimal and anterior nasal mucosal flaps, and every remnant of posterior flaps should be excised during dacryocystorhinostomy.