Acute transverse myelitis may be caused by many factors, however, in most cases the cause cannot be clinically found, which justifies the diagnosis of "Myelitis transversa acuta" or "myelopathia transversa acuta" in such cases. The disease is inflammatory spinal demyelination, differing morphologically from multiple sclerosis. Magnetic resonance is the examination which discloses the injury of several spinal segments. The upper limit of the lesion is higher than the clinical symptoms indicate. There is protein increase and pleocytosis in the cerebrospinal fluid. In most cases the prognosis is favourable; in 33% of patients complete regression of symptoms takes place; 33% present significant improvement and 33% show permanent disability. The frequency of relapses is high and then multiple sclerosis must be suspected. There also occur cases of monophasic multiple sclerosis and relapses of the disease without other symptoms of multiple sclerosis. The treatment of choice are steroids administered in high doses.