Hemophagocytic lymphohistiocytosis (HLH) is a hyperinflammatory condition resulting from an uncontrolled and ineffective immune response. Here, we report a case of HLH caused by disseminated herpes simplex virus (HSV)-1 infection. The patient was initially treated with prednisolone and high-dose acyclovir. Although liver enzymes, coagulation abnormalities, and inflammatory markers were remarkably improved, the platelet count remained low. Prednisolone was therefore switched to dexamethasone palmitate. Thereafter, the platelet count normalized. Inflammatory markers normalized 30 days after admission and serum HSV-DNA became undetectable on day 41. The patient was discharged on day 91 and no developmental delay was evident at 7 months of age. These findings suggest that dexamethasone palmitate is effective for neonatal HLH.