Traditional approaches to disseminating research findings have failed to achieve optimal healthcare. In a systematic review of 235 studies of guideline dissemination and implementation strategies, we observed the following: there was a median 10% improvement across studies, suggesting that it is possible to change healthcare provider behaviour and improve quality of care; most dissemination and implementation strategies resulted in small to moderate improvements in care; multifaceted interventions did not appear more effective than single interventions. The interpretation of our systematic review is hindered by the lack of a robust theoretical base for understanding healthcare provider and organisational behaviour. Future research is required to develop a better theoretical base and to evaluate further guideline dissemination and implementation strategies.