Case report of patient suffering for 3 years of an assumed diffuse lesion of the brain stem. Radiography, iodoventriculography and lumbar perimielography gave the precise diagnosis of an occipitalization of the atlas, subluxation of the odontoid apophysis and Arnold-Chiari's syndrom. Surgical treatment consisted in enlargement of the posterior margin of the foramen magnum and laminectomy of C1, C2 and C3. After 120 days of immobilization in a plaster jacket up to the mandíbula, the patient left the hospital; seven months latter he was examined again, showing the maintenance of the benefic results surgically achieved.