Herpes simplex virus (HSV) remains an important cause of meningitis and encephalitis in adults, and polymerase chain reaction (PCR)-based tests are the "gold standard" for diagnosis. The objective of this study was to assess differences in semiquantitative PCR values, based on the crossing threshold (Ct) value for cases of HSV meningitis and encephalitis. A retrospective chart review was performed for 29 patients with a documented diagnosis of HSV meningitis or encephalitis during the course of 5 years from a large urban academic hospital. Demographic information, cerebrospinal fluid (CSF) laboratory findings, and PCR data were obtained for each patient. There was no statistically significant difference in the Ct values in patients with meningitis or encephalitis. In addition, no differences were found in CSF chemistry and hematology parameters. There is a broad range in relative concentrations of HSV DNA in the CSF in cases of meningitis and encephalitis.