A case of primary amebic meningoencephalomyelitis due to Naegleria sp observed in a 14 years old boy is reported. Symptoms due to myelitis at the dorsal level assumed ascending character during the first days of disease. Manifestations due to encephalic involvemente were discrete. Cerebrospinal fluid changes were marked by pleocytosis, and the eosinophil cells participation in the cytomorptiological profile was persistently high. Amphotericin-B was used intravenously (25 mgm/day) until 1,500 mgm of total dosis. Remission of encephalitic manifestations was prompt, as well as of meningeal signs. Cerebrospinal fluid changes disappeared progressively. Sensitive-motor changes due to spinal cord involvement persisted as permanent sequelae. Naegleria sp., was isolated from the cerebrospinal fluid in the acute stage of the disease, as well as, from the water of a lagoon where the patient used to swimm.