Background: Challenging behaviour, such as self-injury and physical aggression, is an issue of concern regarding a high proportion of individuals with fragile X syndrome. The aim of this review was to provide a comprehensive overview of the topographies and operant functions of challenging behaviours within the syndrome. Method: Five electronic databases were searched, identifying 18 manuscripts. Overall proportions of individuals with particular topographies of behaviour, or behaviour serving different functions, were calculated. Results: Across all participants, biting was the most common form of self-injury for males but not females. A pattern of behavioural function was observed, characterised by high levels of social-negative reinforcement, such as escape from demands. Conclusion: The existence of within-syndrome biases in the manifestation of behavioural challenges is supported by our review.