We report a case with microscopic polyangiitis (MPA) complicated by varicella zoster encephalitis. A 60-year-old woman caught a common cold and had acute otitis media in April 1998. Proteinuria and hematuria with hyaline cast were noted at the routine medical check in May, and she was referred to our hospital because of high fever and chest pain. MPA was diagnosed with acute progressive renal failure, pleuritis and elevated anti-neutrophil cytoplasmic myeloperoxidase antibody (MPO-ANCA). Corticosteroid therapy was administered under hemodialysis but MPA was flared several times with various symptoms including interstitial pneumonitis, alveolar hemorrhage and erythema multiforme exudativum. During the course of the disease she developed disseminated varicella zoster and encephalitis. Positive polymerase chain reaction to varicella zoster in cerebrospinal fluid helped to differentiate her encephalitis from central nervous system symptoms due to microscopic angiitis and herpes simplex encephalitis. Combination of corticosteroid and acyclovir therapies for MPA and varicella zoster encephalitis under hemodialysis were successful. The diagnostic process and therapies to these complicated contexts were thought to be very important.