Twenty patients with myotonic dystrophy underwent neuropsychological evaluation. Performances were analysed with respect to general cognitive profile, family patterns of cognitive impairment, relation with sex, age, extent of muscular involvement, and sex of affected parent. Results showed severe intellectual deficit in 50% of patients and selective impairment of visuospatial and constructional functions. Female patients showed significantly worse global intellectual status than males. No difference in intellectual level was observed in patients with respect to age, extent of muscular involvement and sex of affected parent. No family pattern of cognitive impairment could be identified. Our results show that an extensive neuropsychological battery can reveal the existence of selective mental impairment. It may provide further data on cognitive impairment onset, progression and relation to muscular involvement.