BACKGROUND Receiving negative test results may be associated with two problems: (a). not being reassured and wanting further, unnecessary screening; and (b). not understanding residual risk and not attending future recommended screening. AIM To test two hypotheses: (1). Emphasizing test accuracy and low residual risk when giving negative test results reduces a desire for further unnecessary screening, while also reducing a correct understanding of the meaning of the result. (2). The effect of emphasizing low risk on desire for future screening is mediated by lack of reassurance. DESIGN Experimental, vignette-based study, with a 2 x 2 factorial design. METHOD A sample of 184 women was asked to imagine that they had recently undergone a cervical screening test and received a normal result. They were given one of four hypothetical letters from their GP,differing in whether or not it emphasized test accuracy and low residual risk of developing cervical cancer. Participants completed a questionnaire assessing perceived risk, reassurance about test results, desire for further screening within six months and understanding of the test results. RESULTS Emphasizing test accuracy and low residual risk increases desire for inappropriate screening while reducing the understanding of residual risk. These effects are interactive, in that presenting both together has a larger effect than the sum of the two individual effects. The effect of emphasizing low risk on desire for future screening was mediated by reassurance. CONCLUSION Emphasizing low residual risk and test accuracy is a double-edged sword: it reduces a desire for unnecessary screening, but also reduces correct understanding of the result.