To report a case of primary conjunctival dermoid of the superonasal orbit.

A 41-year-old man complained of swelling of the left lower eyelid and left periocular pain for a week. Examination revealed 3 mm of proptosis with superotemporal displacement of the left eye. Orbital CT revealed a 32×27×33-mm well-defined giant cyst with a fat-fluid level in the superonasal aspect of the left orbit. Orbital MRI showed bone remodeling around the cyst, consistent with a dermoid cyst. The cyst was approached via lateral orbitotomy and transcaruncular incision but was ruptured just prior to the end of the dissection and was totally excised using a cryoprobe to freeze the ruptured site. Upon histopathological examination, the cyst was misdiagnosed as a conjunctival cyst because there was no dermal appendage but was rediagnosed as a conjunctival dermoid cyst after the tissue sample was examined more thoroughly. After surgery, the patient presented with diplopia due to esodeviation and was prescribed prismatic lenses.