The autopsy plays an important role in neoplastic disease. Over one third of all adult autopsies disclose cancer, and clinical diagnostic errors are disclosed in approximately 40% of these. There is no evidence that diagnostic accuracy has improved in recent years. In addition to monitoring diagnostic accuracy--particularly with reference to new technologies--the autopsy is also important in detecting both new types of cancer and new causative agents and patterns of incidence and behavior in "old" types of cancer. It also plays a major role in characterizing the toxic effects of new therapeutic regimens and in establishing true causes of death (including accurate primary cancer sites) for setting local, national, and international research and health care priorities.