This thesis describes correlations between evoked potentials (EPS), magnetic resonance imaging (MRI) and clinical abnormalities in multiple sclerosis (MS). In 31 patients with a cervical cord syndrome, MRI lesions occupying the left or right posterior quadrant of the cervical cord were significantly associated with abnormal somatosensory evoked potentials (SEPs) from the left or right median nerve, respectively. No association was found between brain MRI and SEP abnormalities. MRI and SEPs were only weakly correlated with clinical deficits, except in four cases who had a well localised lesion involving the posterior columns. Brain MRI and hemifield visual evoked potentials (VEPs) were obtained in 15 MS patients with homonymous hemianopia. In each case studied, MRI revealed the presence of large postchiasmal abnormalities which decreased in size in coincidence with visual recovery. VEPs consistent with postchiasmal pathology were recorded in only five cases; latency increase was less frequent than amplitude reduction, which resolved with improvement in the field defect. Among 21 patients with a clinically isolated optic neuritis, the amplitude of the cognitive event-related potentials was significantly attenuated and the performance on psychometric tests assessing relevant cognitive functions significantly poorer in cases with extensive brain MRI abnormalities as compared to those showing fewer lesions. In 11 patients with acute optic neuritis, leakage of Gadolinium-DTPA within the optic nerve lesions was associated with reduction of the VEP amplitude and visual acuity. One month later, the absence of leakage was paralleled by a significant improvement of the VEP amplitude and recovery of the visual acuity. Since gadolinium leakage probably indicates inflammation, the resolution of the latter seems to be an important factor in the recovery from acute optic neuritis. These findings illustrate how the study of the correlation between EP, MRI and clinical abnormalities may improve our understanding of the pathophysiology of MS.