Recent experience suggests that Herpesvirus hominis is the commonest cause of sporadic necrotizing encephalitis in man. We documented H hominis encephalitis in seven patients aged 8 months to 70 years. Five of these seven patients were admitted to our hospital in a 13-month period of time. Four patients were treated with idoxuridine, and three of these died. One patient who received a full course of idoxuridine yielded H hominis from postmortem brain samples in titers approximately equal to those found in the pretreatment brain biopsy specimen. The lone survivor was left with significant neurological deficits. Two patients were treated with cytarabine and, although they remain alive, both are hospitalized in chronic care institutions. The duration and severity of illness manifest by these patients may have adversely affected the outcome of therapy.