In a multicenter study the clinical data of 1271 patients with multiple sclerosis (MS) were recorded in a standardized manner and analysed by a computer program. Some of the retrospective data are compared with previous reports. The frequency of optic nerve involvement in the present series was close to the Japanese figures. The development of signs and symptoms during the course of MS was given for the 1271 patients and differences in the reversibility of symptoms are presented. In this study, one of the chief purposes was the selection of groups of MS patients with particular symptomatology and course of the disease for prospective, detailed study. The following groups were selected and are under further investigation: 109 patients with an exclusively spinal symptomatology throughout the course of their disease; 441 patients with optic neuritis as initial symptom; 110 patients with early brain-stem involvement; 64 benign cases (duration of the disease more than 14 years and disability not more than 3 according to Kurtzke), 35 malignant cases (duration of the disease under 5 years and disability grade of 7 or more); 83 families with more than one member with MS; 289 females with a history of pregnancy, childbirth and/or use of oral contraceptives. In 339 patients a lumbar puncture was performed at the present examination. The parameters determined constitute a pathognomonic pattern highly indicative of the diagnosis of MS.