Multiple sclerosis (MS) with clinical onset after 50 years old is unusual and frequently misdiagnosed. Clinical presentation and course seem also to be different that in MS occurring between 20 and 50 years old. The aim of this study was to evaluate the clinical and paraclinical characteristics of late onset MS. We respectively studied MS patients older than 50 years at the onset of the disease. We evaluated demographical data, clinical symptoms, cerebrospinal fluid (CSF), visual evoked potentials (VEPs) and MRI of these patients. We also studied clinical data during the follow-up with the occurrence of new symptoms and the evolution of the disease by the index of progression (EDSS unit per year). In a population of 1 417 MS, 3.4 p.cent had their first symptoms at 50 years old or older and 0.45 p.cent after 59 years old. At the time of the study patients had more frequently a progressive form: 37 p.cent had a primary progressive form and 35 p.cent a secondary progressive MS. None of the patients with onset after 60 years old had relapsing remittent MS. Motor symptoms were the most common neurologic presentation (54 p.cent of patients). Very few patients had a clinical optic nerve involvement during the follow-up. The mean progression index was 1 suggesting a most severe evolution in this subgroup of MS patients. 76 p.cent of patients had oligoclonal banding detected by CSF electrophoresis. The VEPs were abnormal in 81 p. cent of patients tested. 71 p.cent of the brain MRI were consistent with the diagnosis of MS. 60 p.cent of patients had spinal cord MRI abnormal. This study highlights the differences between the late onset MS and earlier onset. As previously reported, our study underlines the high frequency of progressive course, motor function involvement and poor prognosis.