AIMS: To determine the number of unsuspected disease processes found in a series of cases of sudden unexpected death occurring outside hospital and to enumerate how many of these were not recorded on the death certificate. METHODS: In a series of 1000 routine coroners' necropsies for sudden unexpected death, major findings that had not been known about in life were recorded. Macroscopic findings were confirmed histologically as appropriate. The deaths occurred either outside hospital or in the Accident and Emergency department before the patient could be examined. Cot deaths and decomposed bodies were excluded. RESULTS: There were 575 major findings in 532 (53.2%) subjects that had been clinically silent in life. Of these 575 findings, 277 (48.2%) were not the cause of death and so did not appear on the death certificate. Eighty per cent of the major alimentary system findings and all of the genitourinary findings were of this type. In addition, however, 30% of the major cardiovascular and 34% of the major respiratory findings were not recorded on the death certificate for this reason. CONCLUSIONS: A large amount of important epidemiological data is being lost in the operation of the coronial system. Some of this information is irrecoverable as the function of the death certificate is to provide a cause of death only. In addition, information may be being lost because the necropsy is not being performed adequately and is not subject to audit.