The assessment of depression in people with severe to profound intellectual disability (severe-profound ID) is challenging, primarily due to inability to report internal states such as mood, feelings of worthlessness and suicidal ideation. This group also commonly presents with challenging behaviours (e.g. aggression and self-injury) with debate about whether these behaviours should be considered 'depressive equivalents' or are sensitive for, but not specific to, depression in severe-profound ID. We conducted a systematic review exploring behaviours associated with depression and low mood in individuals with severe-profound ID. The review was conducted in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses (2009) guidelines. Three electronic databases were searched (Embase, PsycINFO and Ovid MEDLINE), and 13 studies were included and rated for quality. Few studies were rated as having high methodological