Lacrimal sump syndrome is an uncommon cause of failed dacryocystorhinostomy. Small osteotomy was reported as the major cause of this syndrome. Here, the authors described the first case of a lacrimal sump syndrome with a large intranasal ostium following endoscopic endonasal dacryocystorhinostomy (EE-DCR). A 51-year-old women patient suffered recurrence of epiphora and dacryocystitis for 8 months following an EE-DCR. Examination showed a large intranasal ostium with a lot of purulent discharge and patent lacrimal irrigation. Lacrimal sump syndrome was diagnosed after passing a probe into the residual lacrimal sac under the aid of an endoscope. The residual sac was reopened and merogel was packed around the wound. The clinical symptoms disappeared after the surgery. It is indicated that lacrimal sump syndrome does happen not only in a small intranasal ostium, but also in a large intranasal ostium. Existing residual sac with bacterial infection may be related to this particular case.