Introduction Various neurologic manifestations have already been described in children during or after severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections. The central nervous system disorders reported in children are mainly encephalopathies during multisystem inflammatory syndrome. We present here an acute meningoencephalitis with cerebral vasculitis associated to a coronavirus disease 2019 (COVID-19) infection in a 13-year-old girl with a 1-year clinical, electroencephalogram (EEG), and magnetic resonance imaging (MRI) follow-up. Case Report A 13-year-old girl presented acute symptoms of consciousness impairment, frontal headache, hyperthermia, and aphasia, with moderate lymphopenia (900/mm3), elevated C-reactive protein (17 mg/L), cerebrospinal fluid (CSF) pleocytosis (15 cells/mm3), slow background with frontal focalization on EEG, a left frontal ischemic lesion, leptomeningeal enhancement, and bilateral limbic fluid-attenuated inversion recovery hyperintensity on cerebral MRI. Reverse transcription-polymerase chain reaction for SARS-CoV-2 was positive in nasopharyngeal swab and COVID serology was positive for immunoglobulin (Ig) M and G, whereas extensive autoimmune antibody investigation was negative except for a positive low titer of anti-myelin oligodendrocyte glycoprotein in CSF and blood. The diagnosis of probable encephalitis associated to cerebral vasculitis after COVID infection was suggested and steroids pulse were started. She recovered within a few days. Six months later, she had moderate clinical sequels including persistent intermittent headaches, an isolated spatial deficit, and focal spikes on the EEG without argument for epilepsia. Conclusion A teenager without previous medical history presented with acute encephalitis with leptomeningitis and vasculitis after a recent COVID-19 infection. Steroids pulse therapy allowed clinical improvement. Cerebral MRI and EEG helped diagnosis, follow-up of the encephalitis, and evolution after treatment.