This study has confirmed a high rate of psychotic symptoms in C9orf72 carriers (64%). Psychotic symptoms are also common in C9orf72 non-carriers (26%). Psychotic symptoms are more severe in C9orf72 carriers than non-carriers. A distributed cortical and subcortical network is associated with increased psychotic symptoms in C9orf72 carriers. The network of affected brain regions is very similar to that seen in other psychotic disorders such as schizophrenia.