Background: Intensive Interaction is an approach used for communicating with people with profound and multiple intellectual disabilities [PMID] or autism. It has gained increased recognition as a helpful technique, but the evidence has not been systematically reviewed. Method: Computerized and hand searches of the literature were conducted using synonyms for "intellectual disabilities", "autism" and "intensive interaction". Results: Fifteen quantitative and three qualitative papers were identified examining the efficacy of the approach with participants across the age range in both educational and residential settings. Conclusions: Studies were limited by the quality of reporting and difficulties conducting good quality, ethically sound research with participants with PMID. Staff support should be considered in training to aid implementation of interventions. Studies attempted to investigate whether Intensive Interaction builds social interactions or reduces repetitive or self-injurious behaviour. More research needs to be conducted before conclusions can be drawn regarding the efficacy of this approach.