Background Herpes zoster ophthalmicus is defined as herpes zoster involvement of the ophthalmic division of the trigeminal nerve. Ocular involvement occurs in 20–70% of patients with herpes zoster ophthalmicus and may include blepharitis, keratoconjunctivitis, iritis, scleritis, and acute retinal necrosis. Orbital apex syndrome is a rare but severe ocular complication of herpes zoster ophthalmicus. We present here the first reported case of herpes zoster ophthalmicus complicated by orbital apex syndrome in a patient from Taiwan. Case presentation A 78-year-old man initially presented with patchy erythema and herpetiform vesicles on his left forehead and upper eyelid. He subsequently developed left-sided ocular complications including reduced visual acuity, anisocoria, ptosis, and complete ophthalmoplegia. Orbital magnetic resonance imaging (MRI) was performed on day 6 of admission to search for signs of the common causes of orbital apex syndrome such as hemorrhage, neoplasm, and cavernous sinus thrombosis. The MRI showed only orbital myositis and enhancement of the retro-orbital optic nerve sheath. The patient was diagnosed with herpes zoster ophthalmicus complicated by orbital apex syndrome. Although the ocular complications partially resolved after systemic antiviral therapy for 15 days and steroid therapy tapered over 12 weeks, there was residual limitation of abduction and paralysis of the left upper eyelid at follow-up at 180 days after the onset of symptoms. The orbital MRI findings at 180 days showed no significant changes compared with the MRI findings on day 6 of admission. Conclusions Primary care physicians should be aware of this rare but potentially sight-threatening complication of herpes zoster ophthalmicus. The appropriate therapy for orbital apex syndrome due to herpes zoster ophthalmicus and the potential outcomes of this condition require further investigation.