OBJECTIVES: To assess the costs of multiple sclerosis (MS) from a sample of 157 French patients followed during 2 years (1 year retrospectively, 1 year prospectively) and consecutively included from June 1995 to December 1996. Costs included health-care consumption, lost earnings and payment of short-term disability benefits by the Social Security. METHODS: At the time of inclusion, the costs of MS were assessed by retrospective interviews covering a one-year period (health-care costs and sick leaves) or since the last consequence of MS on work (loss of earnings). The retrospective data concerning both the health care consumption and sick leaves were completed with prospective data collected by means of a questionnaire during the three-month period following inclusion. Loss of earnings was discounted at 5%. Cost estimates were crossed with medical data at inclusion, and econometric analyses were performed to assess explanatory variables of the health-care costs. RESULTS: Baseline statistics were: mean age, 42.9; women, 66%; secondary progression, 37%; primary progression, 11%; median EDSS score, 5.25. Average one-year retrospective health-care costs (N = 157) amounted to US$7,790.38 (+/-US$9,713.88), with 75.4% going towards hospital costs and 24.6% to ambulatory costs. Main cost items were hospital stay in the neurological ward (29.4% of the total cost) and physiotherapy (15.4%). Three-month prospective healthcare costs (N=101) amounted to US$1,813 (+/-US$2,056), with 56.5% spent on hospital costs. Physiotherapy and drugs were the main ambulatory cost items, accounting for 40.0% and 24.6% respectively of the total prospective ambulatory costs. CONCLUSION: The econometric analysis showed that the health-care costs were positively correlated with the number of years of schooling, the number of relapses, the EDSS score and the Kurtzke sphincter subscore at inclusion, negatively correlated with the Kurtzke sight subscore at inclusion, and were not affected by the form of MS.