A 50-year-old female presented with a slowly enlarging painless mass of the right medial canthus. The past surgical history is significant for external dacryocystorhinostomy for acquired nasolacrimal duct obstruction 10 years prior and subsequent endoscopic and external revisions. Imaging revealed a large fronto-ethmoidal sinus mucocele extending into the right medial orbit. On surgical exploration, the right middle turbinate was found to have lateralized, obstructing sinus outflow. The mucocele was evacuated and ethmoidectomy and middle turbinectomy were performed. The patient did well postoperatively without recurrence at 6 months of follow-up. Sinus mucocele formation is a rare, late complication of lacrimal surgery.