This report describes the unusual diagnosis of a retrobulbar syncytial meningioma in a 16-year-old Thoroughbred gelding. The horse initially presented with unilateral left sided exophthalmos and apparent blindness characterised by unilaterally absent menace and pupillary light responses. Magnetic resonance imaging (MRI) identified a well-defined soft tissue mass intimately associated with the optic nerve. Based on the characteristic MRI appearance, a meningioma was suspected. The eye was enucleated under general anaesthesia and partial excision of the mass was achieved. Histopathology confirmed the diagnosis and the horse underwent a course of adjuvant radiotherapy. Twelve months following surgery the horse is back in work, no neurological abnormalities have been detected and follow-up computed tomographic imaging of the skull has revealed mild bone sclerosis with no remnants of the mass identified.