Progress in medical research has led to an increased number of diagnostic tests. However, the diagnostic accuracy of these tests often lacks evaluation in the primary care setting. Ignorance of evidence-based diagnostic strategies may cause a distorted estimation of diagnostic certainty in general practice and may increase pointless application of diagnostic tests. This study investigates the attitudes of students towards diagnostic accuracy and evaluates whether a seminar about evidence-based diagnosis has an impact on these attitudes. 424 medical students were asked to complete a questionnaire before and after a 90-minute seminar. Before the seminar, 71% of the students thought that due to a lack of resources some diagnostic tests--although necessary--are not being reimbursed. At the end of the seminar, this proportion was reduced by 12% (p<0.001). The call for global reimbursement for all diagnostic tests was reduced by 25% (p<0.001). In contrast, there was no change in the proportion of students (21%) that incorrectly attributed diagnostic uncertainty to a lower competence of the general practitioner. Thus, it seems that after a single seminar there was a cognitive change concerning the application of diagnostic tests rather than a change in the personal attitudes of students towards diagnostic uncertainty in primary care. In this context, the continuous implementation of the principles of evidence-based medicine would be necessary to improve the students' decision-making skills on the basis of a critical attitude including the reasonable handling of uncertainties in medical care.