INTRODUCTION: Magnetic resonance imaging (MRI) has transformed management of patients with multiple sclerosis. The exact contribution of brain MRI remains a subject of debate, but it is generally considered to provide a more specific and more sensitive outcome measure for monitoring purposes and for testing new therapies. The choice of MRI techniques, and measurement reproducibility for multiple sclerosis brain lesions are not defined with precision for routine practice. There are many sources of error when comparing successive images which can be overcome to some extent with repositioning and image processing techniques. METHODS: We evaluated the impact of image repositioning on treatment decision-making for twelve relapsing remitting patients. Brain MRIs were performed every three months for a one-year period. Two neurologists interpreted the non-repositioned and repositioned images giving their analysis of changes in the lesions visualized on the T2 sequences and their therapeutic decisions. RESULTS: For the first neurologist, analysis of the non-repositioned images yielded six patients whose lesions had worsened while for the repositioned images there were only three. For the second neurologist, four patients had more lesions with the non-repositioned images and only three with repositioning. The subjective interpretations were the same for the two neurologists when they used repositioned images. CONCLUSIONS: Comparison by two neurologists of non-repositioned and repositioned MRI, with no other image processing, affected the analysis and in certain cases propositions for treatment.