Cognitive impairment in amyotrophic lateral sclerosis (ALS) is correlated with pathologic and radiographic changes in cerebral cortex beyond the motor regions. Clinically, evidence of impairment can be detected in up to 50 percent of patients through direct neuropsychological testing, although frank frontotemporal dementia (FTD) occurs in a limited percentage. Behavioral changes are also common and can be characterized primarily by the presence of increased apathy. Determining the underlying causes of cognitive or behavioral change may be confounded by several disease-related factors, including fatigue, respiratory compromise, depression, and treatment with medications such as riluzole. Studies assessing the evolution and relative risk for cognitive and behavioral impairment in ALS suggest at least two types of patients: those who have clear FTD in whom cognitive decline develops gradually and those who have mild cognitive or behavioral impairments in whom progression either does not occur or is difficult to detect. Limited data suggest that cognition and behavior influence compliance, management, and survival, although this requires further assessment.