We examined behaviour management problems as predictors of psychotropic medication, use of psychiatric consultation and in-patient admission in a group of 66 adults with pervasive developmental disorder (PDD) and intellectual disability (ID) and 99 controls matched in age, gender and level of ID. Overall, people with PDD had higher rates of most DAS behaviour problems and more frequent use of anti-psychotics than matched controls. Logistic regression analyses showed that physical aggression and problems such as pestering staff independently predicted use of anti-psychotics. Physical aggression and overactivity predicted further involvement of psychiatric services. PDD diagnosis predicted admission to an in-patient unit. The results suggest that externalizing problem behaviours in adults with autism can predict type of treatment intervention.