Benign triton tumor (BTT) or neuromuscular hamartoma is an uncommon tumor composed of mature neural and well-differentiated striated muscular elements. Its development is exceptionally rare in the adult and head region. This report describes a case of adulthood BTT that occurred in the orbit. The patient was a 53-year-old woman who presented with right periorbital swelling and pain in eyeball over 2 months. Magnetic resonance imaging revealed a well-enhancing mass surrounding optic nerve and ocular muscles in the right retrobulbar area. The tumor was subtotally removed via transcranial approach. Its pathological diagnosis was confirmed to be a neuromuscular hamartoma. She developed diplopia postoperatively. Adulthood BTT should be considered in the differential diagnosis of head and neck tumors. It is also important to make adequate therapeutic strategy to avoid postoperative neural dysfunction.