Background: Positive behaviour support (PBS) is behaviour analysis applied in support of people with challenging behaviour. Questions have been raised as to PBS effectiveness, costs, and accessibility. Method: Outcome studies meeting specified criteria for PBS were selected for review. All told, 12 outcome studies encompassing 423 cases were included. Results: This review showed that PBS was effective with both severe and high-rate behaviour problems, was cost-effective, used a methodology that was easily trained and widely disseminated, and worked in institutional settings in which the most difficult problems are thought to be, as well as in the community. Conclusions: The major implication of this review is that practitioners may be obligated to use PBS when faced with the need to develop a plan of support given the ethical principle of using the least restrictive method consistent with the right to effective treatment. (Contains 1 figure and 1 table.)