Background. During the past few decades, hospital autopsy rates have steadily declined throughout the Western world. This decline is mainly attributed to the introduction of advanced diagnostic techniques. Despite technological developments, discrepancy rates between clinical diagnoses and autopsy findings remain high. Few studies have addressed discrepancy rates exclusively with regard to malignant neoplasms. In the present study, we reviewed the records of 3,118 autopsies performed at Mayo Clinic during a 6-year period (1994–1999) and identified clinically undiagnosed malignancies found at autopsy and clinically diagnosed cancers not confirmed at postmortem examination. Materials and Methods. Autopsy protocols, provisional and final anatomic diagnoses, and data from the Mayo Autopsy Pathology Quality Assurance program were reviewed in an attempt to identify discrepancies between clinical diagnoses and autopsy findings regarding malignant neoplasms. Results. In 3,118 autopsies performed at Mayo Clinic between 1994 and 1999, a malignant tumor was identified in 768 cases (25%). In 128 of 3,118 cases (4.1%), the malignancy was not diagnosed clinically. In 14 of 3,118 cases (0.45%), autopsy failed to confirm a clinically diagnosed cancer. A review of the literature is presented. Conclusions. Autopsy remains an effective tool for the confirmation and refutation of clinical diagnostic findings regarding malignant neoplasms.