Cognitive deficits are present in a substantial number of Multiple Sclerosis (MS) patients, particularly in those with the chronic-progressive type of the disorder. We assessed cognitive decline and its relationship with T2-weighted images on magnetic resonance imaging (MRI). We submitted a group of 26 patients with progressive MS to both MRI and a battery of neuropsychological tests. Cognitive impairment did not correlate with duration of illness or severity of neurological disability, but rather with the presence of extensive periventricular demyelination on MRI, evaluated as area of confluent lesions. These results suggest that cognitive deficits in MS represent a symptom of disease and not a parallel occurrence.