OBJECTIVE: The presentation format of clinical trial results, or the 'frame,' may influence perceptions about the worth of a treatment. The extent and consistency of that influence are unclear. We undertook a systematic review of the published literature on the effects of information framing on the practices of physicians. DESIGN: Relevant articles were retrieved using bibliographic and electronic searches. Information was extracted from each in relation to study design, frame type, parameter assessed, assessment scale, clinical setting, intervention, results, and factors modifying the frame effect. MAIN RESULTS: Twelve articles reported randomized trials investigating the effect of framing on doctors' opinions or intended practices. Methodological shortcomings were numerous. Seven papers investigated the effect of presenting clinical trial results in terms of relative risk reduction, or absolute risk reductions or the number needing to be treated; gain/loss (positive/negative) terms were used in four papers; verbal/numeric terms in one. In simple clinical scenarios, results expressed in relative risk reduction or gain terms were viewed most positively by doctors. Factors that reduced the impact of framing included the risk of causing harm, preexisting prejudices about treatments, the type of decision, the therapeutic yield, clinical experience, and costs. No study investigated the effect of framing on actual clinical practice. CONCLUSIONS: While a framing effect may exist, particularly when results are presented in terms of proportional or absolute measures of gain or loss, it appears highly susceptible to modification, and even neutralization, by other factors that influence doctors' decision making. Its effects on actual clinical practice are unknown.