Twenty-two patients with polymyositis and dermatomyositis (PM-DM) were retrospectively studied with regard to development of herpes zoster. Herpes zoster occurred with high frequency in patients with PM-DM. The clinical courses of zoster infections were uneventful; no severe complications nor deaths occurred, and only one patient had post-therapeutic neuralgia. No specific therapy for this infection was necessary. Zoster tended to occur in the inactive stage of PM-DM. PM-DM patients with herpes zoster had a significantly higher incidence of antinuclear antibody. There seemed to be no relationship between steroid therapy and herpes zoster infection.