A systematic investigation of the cognitive functions of 22 patients affected with motor neuron disease (MND) compared to 36 controls matched for age and education was performed. The MND group showed cognitive performances slightly but significantly lower than the control group; 6 MND patients, however, had decidedly pathological values. Cognitive impairment was stereotyped and global, with sparing of memory. There was no significant difference between patients with isolated involvement of the lower motor neuron and those with associated pyramidal involvement. Our neuropsychological findings are in agreement with previous clinical, neuroradiological and pathological reports indicating extra-motor cerebral involvement in MND.