Wegener's granulomatosis can involve the orbit and sometimes the optic nerve. This usually occurs as a result of contiguous spread from affected sinuses or extraocular muscles, or from a vasculitic posterior optic neuropathy. However, we present an unusual case of isolated orbital apex infiltrative disease in a patient with known Wegener's granulomatosis. This initially caused painless optic neuropathy and progressed to painful ophthalmoplegia and blindness. Optic nerve biopsy, performed to exclude methotrexate-induced lymphoma, confirmed optic nerve infiltration. The condition was refractory to high-dose pulsed methylprednisolone but the patient gained symptomatic relief from rituximab. Wegener's granulomatosis should be considered in cases of isolated posterior optic neuropathy, and close attention should be placed on imaging the orbital apex.