A 7-year-old boy with no prior illness or altered immunity presented to the emergency department with a 36-hour history of fever (103.7°F), emesis, headache, and lethargy. The patient had a history of swimming in a local lake the week before presentation. Physical examination revealed nuchal rigidity. Computed tomography (CT) of the head was normal. A lumbar puncture revealed a cerebrospinal fluid (CSF) protein of 670 mg/dL, glucose of 23 mg/dL, 265 red blood cells/mm3, and 308 white blood cells/mm3. The Giemsa-stained differential consisted of 54% polymorphonuclear leukocytes, 4% bands, 39% lymphocytes, and 1% monocytes. Numerous organisms were also identified that were consistent with Naegleria fowleri. Wet-mount preparation of fresh CSF confirmed the organism's characteristic swift motility. CSF culture and real-time PCR testing (Centers for Disease Control and Prevention) were positive for Naegleria fowleri and excluded Entamoeba histolytica.