The current literature recognizes two antigenic types of herpes simplex virus, type 1 and 2. Type 1 is the most common cause of sporadic necrotizing encephalitis in the United States, with a mortality rate of 30 to 70 percent, and leaves various neurologic sequelae in the survivors. Herpes simplex virus type 2 has been recognized as an etiologic agent in fatal infections in neonates and a mild meningitis in adults, but its role in encephalitis in adults is less well known. We report a case of herpes simplex virus type 2 encephalitis with an analysis of four additional cases previously documented in the literature. Herpes simplex virus type 2 may cause more infections than is presently recognized, and we suggest that some cases of acute psychosis may, like in our case, represent herpes simplex virus type 2 encephalitis.