In the present study 100 randomly selected autopsies from each of the years 1959, 1969, 1979, and 1989 at a German university hospital were analyzed to determine whether advances in diagnostic procedures have reduced the misdiagnosis rate. We define misdiagnosis as occurring when a disease that does not exist is assumed to be present and when the failure to recognize the true existing disease leads to a worsened patient prognosis. In all years analyzed, about 10% of the autopsies revealed a misdiagnosis; another 25% disclosed a false negative diagnosis; which did not influence the patient's prognosis; and about 10% disclosed a false-positive diagnosis, which again did not influence the patients prognosis. The most common diagnostic errors were pulmonary emboli, myocardial infarctions, neoplasms, and infections. The introduction of new diagnostic procedures such as ultrasound, computerized tomography, and radionuclide scans has not reduced the rate of misdiagnoses. Misinterpretation, technical errors, and overreliance on these new procedures occasionally contributed directly to diagnostic errors. By contrast, the patient's medical history and physical examination played an important role in the diagnostic process, leading to a correct final diagnosis in 60%-70% of cases.