A fourteen year old girl who had developed a large subconjunctival mass extending into the orbit is presented. The mass had appeared after a strabismus operation, and it caused a consecutive exotropia and decreased adduction in the affected eye. She had had this cyst for six years. A cranial CT scan confirmed the presence of a massive orbital cyst. This cyst was removed surgically. Postoperatively, exotropia and adduction limitation improved. The pathological report stated that it was an epithelial cyst. This cyst and its differential diagnosis is the subject of this paper.