Cognitive impairment in patients with amyotrophic lateral sclerosis (ALS) is well documented, but behavioral abnormalities are not well defined. The Frontal Systems Behavior Scale (FrSBe) was used to assess changes in apathy, disinhibition, and executive dysfunction in 45 patients with ALS. Results suggest a high incidence of behavioral change, most notably in apathy associated with the onset of the disease and independent of mood. Apathy and verbal fluency were correlated, lending further support to the hypothesis that an underlying continuum exists between ALS and frontotemporal dementia (FTD), which is characterized predominantly by behavioral disturbance. The FrsBe is useful for detecting behavioral change and abnormalities in patients with ALS.