Amyotrophic lateral sclerosis (ALS) has traditionally been assumed to be a purely motor disturbance. It is now recognized that 2-5% of patients with ALS develop frontotemporal dementia. Additionally, neuropsychological analysis and functional imaging suggest that a proportion of patients with classical ALS also have neuropsychological impairment. On postmortem examination, ALS patients classified as not demented showed atrophy of the frontotemporal cortex. Conversely, in patients with frontotemporal dementia without known motor impairment, atrophy of spinal and bulbar neurons were found on postmortem examination. It is still not known whether patients with ALS and neuropsychological impairment form a distinct subgroup or if they are part of a continuous spectrum that runs from pure motor impairment to pure neuropsychological impairment.