The case that we report occurred in a previously healthy, fully immunized 13-year-old female presenting with severe unilateral headaches and generalized tonic-clonic seizures and subsequently diagnosed with herpes simplex virus type 1 (HSV-1) meningoencephalitis. The patient was successfully treated with acyclovir and seizures were controlled with valproic acid. The HSV meningoencephalitis has high morbidity and mortality. Our case highlights one of the severe presentations of HSV meningoencephalitis in young adolescents that can manifest with headaches, fever, seizures, focal neurologic signs, and altered mental status. We also highlight the need for a thorough workup among pediatric providers in the emergency and inpatient departments to avoid delays in diagnosis that can lead to poor outcomes.