Cognitive dysfunction frequently occurs during the course of multiple sclerosis (MS). In patients with MS the severity of cognitive manifestations is not closely related to indices of structural brain damage. Neuroplasticity may contribute to the maintenance of normal performance despite scattered brain lesions. Changes in functional organization of the cerebral cortex have been reported by functional magnetic resonance imaging (fMRI) studies in MS. fMRI studies provide an interesting way of understanding how the brain changes its functional organization in response to MS, and might be useful in the study of the effects of rehabilitative or pharmacological therapy on brain plasticity. The purpose of this review is to examine major fMRI studies focusing on cognitive dysfunction in MS.