BACKGROUND Orbital compartment syndrome is a rare ocular emergency requiring immediate intervention to prevent vision loss. It can arise due to a variety of causes including trauma, neoplasms and retrobulbar hemorrhage during endoscopic sinus surgery. Lateral canthotomy and inferior cantholysis is a well-known therapeutic procedure to rapidly relieve raised intraocular pressures. METHODS We report a case of a subperiosteal orbital abscess due to acute maxillary sinusitis that underwent endoscopic drainage. Intraoperatively, he developed raised intraocular pressure following irrigation of the maxillary sinus and manual pressure on the malar abscess, necessitating emergent lateral canthotomy and inferior cantholysis. CONCLUSIONS To our knowledge, this is the first reported case of orbital compartment syndrome following sinonasal irrigation and malar pressure in the English literature. This case will serve as a reminder to the sinus surgeon of the potential danger of transmitted pressure from the paranasal sinus or malar soft tissue into the orbital compartment.