We evaluation of the role of determining the distribution of brain-stem, cerebellar and cerebral lesions in number and volume by MRI in determining the efficiency of treatment of multiple sclerosis (MS). We studied 24 patients diagnosed as having relapsing and remitting MS, of whom 12 received intravenous immunoglobulin G; a control group of 12 were given placebo. In a double-blind study, MRI was obtained initially and at 3, 6 and 9 months, and interpreted without knowledge of clinical findings, laboratory tests or treatment. The lesions were classified according to their distribution and evaluated qualitatively and quantitatively. Each patient was also examined clinically and scored according to the expanded disability status scale (EDSS) following every MRI examination. All patients in the treatment group showed significant improvement. The lesions decreased in both in size and number in all sites. In the control group lesions increased both in number and size in all sites, but only the increase between 3 and 6 months was statistically significant. In both groups, significant apparent changes were detected in the cerebellum and brain stem. Volumetric evaluation was found to be more helpful than qualitative assessment. © Springer-Verlag 2004.