In previous reports on the viral causes of central nervous system (CNS) 
infections, it has been generally recognized that HSV-1 is a major cause of 
encephalitis, while HSV-2 is the predominant cause of aseptic meningitis in 
adults. To examine this matter, the clinical characteristics in the two types of 
HSV CNS infections were investigated. In a retrospective cohort study which 
included all adult patients (≥16 years) between January 1999 and December 2013 
in a 2,700-bed tertiary care hospital, all the patients in whom PCR of the CSF 
for HSV was positive were identified. Ninety-five patients with positive CSF PCR 
results for HSV were included, 21 with HSV-1 and 74 with HSV-2. Many patients 
with HSV-1 had encephalitis (13/21, 61.9%), whereas most patients with HSV-2 had 
meningitis (62/74, 83.8%). However, HSV-1 and HSV-2 accounted for similar 
proportion of patients with HSV encephalitis (13/25, 52.0% vs. 12/25, 48.0%). 
Neurological sequelae were more frequent among patients with HSV-1 (9/21, 42.9% 
vs. 6/74, 8.1%; P = 0.001). The present study suggests that HSV-2 is not only a 
major cause of aseptic meningitis, but also it may cause serious manifestation 
as HSV-1 encephalitis in adults.