Isolated amnesia is an uncommon presenting complaint in the pediatric age group. We report the case of an 18-year-old woman who presented with the acute onset of memory difficulty and an otherwise normal neurologic examination. Brain magnetic resonance imaging demonstrated inflammation in the bilateral temporal lobes. Serum and cerebrospinal fluid testing ultimately revealed a diagnosis of autoimmune encephalitis. Although rare, the acute onset of isolated amnesia deserves a prompt, comprehensive evaluation.