Orbital apex syndrome (OAS) is an optic nerve dysfunction with palsy of the third, fourth and sixth cranial nerves and ophthalmic division of the fifth cranial nerve. Causes can be infective, inflammatory, traumatic, neoplastic or vasculitic. We describe the first case in British literature and second worldwide of OAS presenting as granulomatosis with polyangiitis (GPA). A 38-year-old patient presented with left periorbital swelling and pain. An examination revealed left eye proptosis, tenderness in the ophthalmic distribution of the trigeminal nerve, unilateral ophthalmoplegia and reduced visual acuity. Initial treatment included intravenous antibiotics, steroids and nasal decongestants.Imaging demonstrated sinusitis and a suspected abscess from the infratemporal fossa to the orbital apex. However, sinus surgery showed granulation tissue without pus. The biopsy result was highly suggestive of GPA. A subsequent vasculitic screen was cytoplasmic-antineutrophil cytoplasmic antibody positive.This case highlights an unusual presentation of OAS secondary to GPA, as initial features suggested an infective cause.