In medical clinic visits, patients do more than convey information about their symptoms and problems so doctors can diagnose and treat them. Patients may also show how they have made sense of their health problems and may press doctors to interpret their problems in certain ways. Using conversation analysis, we analyse a practice patients use early in the medical visit to show that relatively benign or commonplace interpretations of their symptoms are implausible. In this practice, which we term pre-emptive resistance, patients raise candidate explanations for their symptoms and then report circumstances that undermine these explanations. By raising candidate explanations on their own and providing evidence against them, patients call for doctors to restrict the range of diagnostic hypotheses they might otherwise consider. However, the practice does not compel doctors to transparently indicate whether they will do so. Patients also display their ability to recognise and weigh the evidence for common, easily remedied causes of their symptoms. By presenting evidence against them, they show doctors the relevance of more serious diagnostic interpretations without pressing for them outright.