The randomised controlled trial (RCT) is widely acknowledged as the "gold standard" in the evaluation of clinical interventions. Recruitment, however, is often problematic, with serious implications for the detection of important treatment differences, the generalisability of research findings to other patient populations and cost. A recent review demonstrated that less than a third of UK studies recruited the required sample size within the timeframe originally specified, and approximately one third required an extended recruitment period. The recruitment and retention of participants is particularly problematic in critical care research, the rationale for which is currently ill-defined.