Multiple sclerosis presenting at onset with clinical signs and CT picture suggesting a cerebral neoplasm or a slowly evolving stroke, is uncommon. We report one patient in whom cerebral tumour was suspected not only clinically but also from CT features. M.R.I., demonstrating multifocal, high intensity, unsuspected periventricular and white-matter lesions, permitted to diagnose what seemed an intracranial left parietal neoplasm as an acute plaque of demyelination. In fact, in the follow-up, this large low-intensity left parietal area acquired structural and volumetrical homogeneity compared to all other present hyperintense lesions. Instead multimodal EPs, though disclosing subclinical dysfunction in the early stage of the disease, did not correlate with changes in neurological examination to follow-up. So they, unlike the M.R.I., seem of no particular usefulness to serially monitor the clinical modification of MS.