<p>Traditionally, amyotrophic lateral sclerosis (ALS) has been defined as a rapidly progressive neurodegenerative disorder that affects the large motor neurons of the brain and spinal cord. The assumption that ALS is a pure motor disorder has been increasingly challenged by accumulating evidence about an association between ALS and psychiatric disorders. They often precede the onset of motor symptoms or psychoses; hallucinations and schizophrenia may occur as concomitant changes. These non-motor disorders have a close relationship with disease onset or may be related to a larger framework of neuronal network disruptions in motor neuron disorders. The link between ALS and schizophrenia was supported by substantial genetic correlations associating the <i>C9orf72</i> gene expansion with psychiatric disorders. The genetic correlation between ALS and schizophrenia was estimated to be 14.3% with frequent polygenic risk scores. Increased psychotic symptoms in <i>C9orf72</i> carriers correlate with atrophy in a distributed cortical and subcortical network that includes multiple cerebral regions. ALS kindreds often present higher rates of psychiatric illnesses, and early schizophrenia is significantly associated with the development of ALS. Further studies should attempt to delineate the risk of psychiatric disorders in <i>C9orf72</i> kindreds to aid in clinical decision making and genetic counseling, through collaborations between neurology and psychiatry.</p>