Fragile X Syndrome (FXS) appears to be associated with an increased risk for engaging in challenging behaviour, particularly self-injury, relative to those with mixed aetiology learning disabilities. Such behavioural issues are reported to be of high concern for those providing support. As such, this systematic review aimed to gain further epidemiological data regarding challenging behaviours in individuals with FXS, including: self-injurious behaviour (SIB), hand-biting as a specific topography of SIB, aggression and property destruction. Twenty eight manuscripts were identified which reported the prevalence of a relevant topography of behaviour, with widely varying prevalence estimates. Weighted averages of the prevalence of behaviours were calculated across studies. Comparison of proportions revealed significant gender differences and differences in the prevalence of types of behaviour. It is hoped that this comprehensive overview of data on this clinically significant topic will help to inform and drive future investigation to understand and provide effective intervention for the benefit of those with FXS.