Although the term of amyotrophic lateral sclerosis (ALS) is often used interchangeably with motor neuron disease, ALS is universally accepted as a multisystem disorder. Cognitive impairment is an acknowledged feature of ALS, affecting language, memory and behaviour, and apathy is considered to be the prevalent behavioural alteration in ALS. It can be divided in three subtypes: executive, emotional and initiation apathy. Out of the three subtypes, initiation apathy is common among patients with ALS. Even in patients that do not meet the criteria for ALS with frontotemporal dementia, low-key neuropsychiatric and cognitive changes can be observed. Apathy has also been found to be systematically associated with disruptions in medial frontal cortex and subcortical structures in several neuroimaging studies that confirm the pre-existing brain lesions in the early stages of this disease. Thus, there is a growing body of evidence that motor signs and symptoms are accompanied or even preceded by cognitive and behavioural alterations, and screening for non-motor signs and symptoms can be clinically relevant.