A comparison of mortality from ischaemic heart disease under the age of 60 for 1980 to 1981 between the Grampian Health Board and the North Staffordshire Health Authority has been made. A total of 993 deaths was notified by death certificate from the two areas of similar population of which 434 were from Grampian and 559 from North Staffordshire. After examination of general practitioner and hospital case notes, autopsy reports and death certificates, nearly all (532) of the North Staffordshire deaths were accepted as being due to ischaemic heart disease but only three-fifths (263) of the Grampian deaths could be substantiated as there was inadequate information for the remainder. Deaths from ischaemic heart disease seem apparently to be twofold greater in North Staffordshire than Grampian but much of this discrepancy could be attributed to a widely different autopsy rate and to unavailability of case notes. Experience of this survey suggests that the results of other epidemiological investigations may be equally or even more unreliable.