The way clinicians break bad news to cancer patients has been retrospectively associated with poor psychosocial outcomes for patients. Education and practice in breaking bad news may be ineffective for improving patients' well-being unless it is informed by a sound evidence base. In the health field, research efforts are expected to advance evidence over time to inform evidence-based practice. Key characteristics of an advancing evidence base are a predominance of new data, and rigorous intervention studies which prospectively demonstrate improved outcomes. This review aimed to examine the progress of the evidence base in breaking bad news to cancer patients. Manual and computer-based searches (Medline and PsycINFO) were performed to identify publications on the topic of breaking bad news to cancer patients published between January 1995 and March 2009. Relevant publications were coded in terms of whether they provided new data, examined psychosocial outcomes for patients or tested intervention strategies and whether intervention studies met criteria for design rigour. Of the 245 relevant publications, 55.5% provided new data and 16.7% were intervention studies. Much of the intervention effort was directed towards improving provider skills rather than patient outcomes (9.8% of studies). Less than 2% of publications were rigorous intervention studies which addressed psychosocial outcomes for patients. Rigorous intervention studies which evaluate strategies for improving psychosocial outcomes in relation to breaking bad news to cancer patients are needed. Current practice and training regarding breaking bad news cannot be regarded as evidence-based until further research is completed.