Background: Dual diagnosis (DD) refers to the coexistence of intellectual disability and psychiatric disorder. In order to provide individuals with DD with adequate care, it is essential for mental health workers to have adequate knowledge and positive attitudes. These may be achieved through proper training. Aims: To summarise the available literature examining the knowledge, attitudes and training of psychiatrists and other professional caregivers in regard to serving people with DD. Methods: A search strategy was developed to find manuscripts published in English since 1995. Results: Twenty-seven studies on knowledge, attitudes and training in the field of DD were identified and reviewed in this paper. Conclusion: The findings of this review stress the need to improve the knowledge, competence and attitudes of practitioners within the DD field via training and practice opportunities. In light of this review, recommendations for improving training opportunities and for conducting future research are made.