Background: Aggressive behaviour is prevalent in people with intellectual disabilities. To understand the aetiology, it is important to recognize factors associated with the behaviour. Method: A systematic review was conducted and included studies published between January 2002 and April 2017 on the association of behavioural, psychiatric and psychosocial factors with aggressive behaviour in adults with intellectual disabilities. Results: Thirty-eight studies were included that presented associations with 11 behavioural, psychiatric and psychosocial factors. Conflicting evidence was found on the association of these factors with aggressive behaviour. Conclusions: The aetiology of aggressive behaviour is specific for a certain person in a certain context and may be multifactorial. Additional research is required to identify contributing factors, to understand causal relationships and to increase knowledge on possible interaction effects of different factors.