Sixty-two consecutive patients with clinically definite multiple sclerosis (MS) were classified into 2 subgroups: group A, consisting of 16 patients who had shown acute transverse myelopathy (ATM) during the course of illness; and group B, 46 patients without ATM. The clinical features of these 2 groups were analysed prospectively for certain periods, and some significant differences were found. There was (1) later onset, (2) less frequent occurrence of brain stem, cerebellar and cerebral symptoms, (3) more frequent and severe involvement of the optic nerve, (4) a smaller proportion of patients with abnormal findings on brain MRI in group A compared with group B. The clinical features of group B were quite similar to those of previous Western series, while group A seemed to constitute a distinct clinical subgroup in patients with MS.