An adult, female, free-ranging, sika deer (Cervus nippon yakushimae) from Wicomico County, Maryland, USA, was found circling and having no fear of humans. The animal was euthanized and submitted for a postmortem exam. There were no gross lesions and the deer was negative for rabies. Microscopic examination revealed lymphoplasmacytic, neutrophilic, and eosinophilic meningoencephalitis with intralesional adult nematodes, larvae, and eggs consistent with nematodes in the family Protostrongylidae. Parelaphostrongylus tenuis was identified by polymerase chain reaction and DNA sequencing. To our knowledge, this is the first report of P. tenuis–associated encephalitis in a sika deer.