Background Herpes simplex encephalitis (HSE) is the most common form of sporadic encephalitis which is caused by herpes simplex virus type 1 (HSV1). Current guidelines recommend intravenous Acyclovir for 14 to 21 days in cases of HSE. Objective Optimizing the Acyclovir treatment duration is important in regards to preventing Acyclovir related neurotoxicity and nephrotoxicity. Study design We retrospectively evaluated 13 patients, who were diagnosed with HSE by molecular testing (HSV1 PCR positivity in cerebrospinal fluid), in two university hospitals in Istanbul, between 2010 and 2021. The patients were treated either 10 days or less as a short term treatment regimen of Acyclovir or for 14 days or more as long term treatment regimen Results The median age was 58 years (range 24 to 82 years) and 54% of them were male. The median follow up time was 79 days (range 20 to 670 days) after discharge. Long-term treatment was used in 6 and a short term treatment regimen was used in 7 cases. One of the patients died on the 4th day of Acyclovir treatment. One patient never received Acyclovir treatment. Of the 5 patients who received long-term treatment, 3 (21 to 28 days) had amnesia and orientation cooperation restriction, one (21 days) died on the 2nd day of treatment, while the other (14 days) had no sequelae. There were no sequelae in three out of 5 patients who received short-term treatment. Conclusions We believe that it is necessary to determine the optimal Acyclovir therapy duration should be evaluated in a prospective randomized clinical trial in large patient population.