Cognitive functions were investigated in 37 patients with myotonic dystrophy (MD) and correlated with clinical and neuroradiological variables. The whole cognitive performance was at a low-average level; in about 1/3 of the subjects, in fact, the scores at the neuropsychological tests were below the normal range. There was a consistent trend for patients with inheritance on maternal side to perform worse on Wechsler verbal score and to present cerebral atrophy. In 7 out of 12 subjects focal white matter lesions were found at nuclear magnetic resonance. The significance of these findings and its relation to cognitive performance are discussed.