Background: Although our understanding of dual diagnosis has improved, a deficit still exists in our knowledge of how schizophrenia spectrum disorders (SSD) manifest themselves in individuals with intellectual disability (ID). In addition, little is known about the relationship between behaviour problems and psychopathology in this population. Method: Utilising the "Behavior Problems Inventory" (BPI), three areas of problem behaviour (self-injurious, stereotyped, and aggressive/destructive) were assessed in 58 individuals with ID divided into three groups (with SSD, with a diagnosis of psychopathology other than SSD, and with ID only) and a total BPI score was calculated for each. Results: The SSD group was unique when compared to the Control group (ID only) for frequency of stereotyped behaviours. Further, severity of stereotyped behaviours in the SSD group was unique compared to the Psychopathology and Control groups. Conclusion: The SSD group was unique compared to the other two groups, particularly for severity of stereotyped behaviours. Many specific behavioural differences were also related to either SSD or general psychopathology. (Contains 3 tables.)