INTRODUCTION: Progressive outer retinal necrosis (PORN) is a rare but devastating infectious retinitis associated with varicella zoster virus (VZV) and responsible for severe visual loss. CASE REPORT: A 59-year-old man treated for generalized myasthenia with oral azathioprine and prednisone presented with severe unilateral necrotizing retinitis. Polymerase chain reaction of the aqueous and vitreous humors was diagnostic for VZV PORN. CONCLUSION: VZV PORN is a severe potential ocular complication of immunosuppression, prompting urgent diagnosis and appropriate treatment.