Neuropsychological functioning was compared between 7 myotonic dystrophy (MD) patients with maternal inheritance (mMD), 14 MD patients with paternal (pMD) inheritance, and 10 normal controls. Both groups evidenced slowed performance on a measure of information processing speed. However, the pMD group had an otherwise normal neuropsychological profile. In contrast, the mMD group exhibited abnormal scores on measures of intelligence, visual-construction, and some, albeit not all, measures of frontal functioning. No significant differences between the three groups were detected on measures of verbal or visual memory, or on measures of visual-perception. Overall, these findings suggest that inheritance pattern is one important moderating variable in determining the impact of the MD gene on cognitive functioning. Personality assessment revealed a relatively high incidence of dependent tendencies and depressive symptoms, even among pMDs. Given the generally normal cognitive functioning among pMDs, personality/emotional disturbance observed among MD patients may largely reflect their adjustment to having a progressively disabling medical condition, rather than being a direct expression of MD related brain dysfunction.