The frequency of multiple sclerosis in Brasil is assumed to be lower than in some geographically comparable regions, but internationally available objective diagnostic criteria are not generally used. We have reviewed a number of such criteria and applied those of Poser and colleagues to all patients who could be examined specifically for this study; who had been under our care between 1982-87; with clinically satisfactory history, physical exam, ancillary investigations and follow-up; with enough information to warrant immunosuppressive therapy with azathioprine, methyl-prednisolone or cyclophosphamide. There were 35 (88%) females and 5 (12%) males, with clinically definite (85%), probable (10%) disease according to Poser and cols, as well as 2 patients with chronic progressive disease. Age at time of study was 39 ± 11 years, age at onset had been 32 ± 10 years, and length of history was 6 ± 7 years (mean ± sd). Mode of onset was a disturbance of gait in 50%, of vision in 25% and dizziness in 10%. Physical exam at time of study showed motor deficits in 92.5%, sensory in 67.5%, ocular visual in 65%, spastic bladder in 35%, and vestibulocerebellar disturbances in 32%. Visual evoked responses were abnormal in 65% of 31 cases, auditory in 23% of 22 cases, and somatosensory in 80% of 20 cases. This study shows that international diagnostic criteria, specifically those of Poser and colleagues are applicable in Brasil, providing clear guidelines for diagnosis of multiple sclerosis. We suggest objective diagnostic criteria form the backbone of teaching about the disease, at various levels of medical education. Their wide utilization will in due time provide conditions for epidemiological, clinical and therapeutic studies which have not as yet been carried out in this country.