One hundred and seven cases of herpes zoster in a hospitalized population with a variety of illnesses during a 20 year period were reviewed. Zoster occurred throughout the year, without seasonal predominance, and was most frequent in lymphoproliferative malignancy. In the majority, lesions were confined to the skin in one or more adjacent dermatomes (localized zoster) and were most frequent in the thoracic region. In 15 per cent of the cases, cutaneous dissemination of the lesions developed; this occurred four to 11 days after the onset of dermatomal lesions, and in one-third of these there was central nervous system involvement. Dissemination of zoster, however, directly resulted in only one death. Predisposing factors for zoster included local irradiation and, occasionally, surgery in subsequently involved areas. There were trends for more frequent splenectomies in patients with Hodgkin's disease in whom zoster subsequently developed, and for more frequent corticosteroid therapy in patiens with disseminated zoster. Advanced stage of Hodgkin's disease, in itself, was not associated with development of zoster, and the onset of zoster did not herald a poor prognosis for the underlying disease. Herpes zoster was, thus, largely a source of increased morbidity rather than mortality in the population studied, and multiple factors appeared to predispose to the development of zoster in this group of patients.