BACKGROUND There are many barriers to patient participation in randomised controlled trials (RCTs) of cancer treatments. To increase participation in trials, strategies need to be identified to overcome these barriers. The National Cancer Research Network (NCRN) commissioned a systematic review of the evidence-base for interventions to increase cancer patient participation in trials. AIM To evaluate the effectiveness of interventions to overcome barriers to participation in RCTs of cancer treatments. METHODS Fifteen electronic databases including MEDLINE, EMBASE, PsycINFO, and System for Information and Grey Literature in Europe, and Science and Social Science Citation Index were searched from inception to January 2005 for published and unpublished studies in any language. Bibliographies of potentially relevant articles were searched. Two reviewers independently assessed titles and abstracts and also full papers where these were obtained. Studies of any interventions to improve cancer patient participation in RCTs, which reported participation rates, were eligible for inclusion. RCTs and non-RCTs as well as before and after studies reporting baseline rates specific to the population being investigated were included. Data were extracted by one reviewer into structured summary tables and checked for accuracy by a second reviewer. Each included study was assessed against a checklist for methodological quality by one reviewer and checked by a second reviewer. A narrative synthesis was conducted. Studies were grouped according to relevance to the UK setting and within this by study design. RESULTS Eight studies were identified that met the inclusion criteria: three RCTs, two non-RCTs and three observational studies. Six of the studies had an intervention that had some relevance to the UK. The majority of studies were concerned with some aspect of the consent process. There was no evidence that any of the interventions investigated led to an increase in cancer patient participation in RCTs, though one good quality RCT found that urologists and nurses were equally effective at recruiting participants to a treatment trial for prostate cancer. Although there was no evidence of an effect in any of the studies, the evidence was not of sufficient quality to be able to conclude that these interventions therefore do not work. Overall, the studies had a range of methodological weaknesses. In particular, in most of the studies there was a risk of contamination between the experimental and comparison intervention leading to a possible dilution of the effect of the experimental intervention. CONCLUSIONS There is not a strong evidence-base for interventions that increase cancer patient participation in randomised trials. Further research is required to evaluate the effectiveness of strategies to increase participation in cancer treatment trials.