We estimated the reporting of diabetes on death certificates for persons known to have diabetes. Surveillance of 19 hospitals and two paramedic emergency medical services during 12 months in Seattle and King County, Washington, ascertained acute ischemic heart disease events for persons with diabetes and yielded 1235 persons with suspected ischemic heart disease. Mortality was 23.6%, and 41% of death certificates listed diabetes. The reporting of diabetes on the death certificate was not random, and it varied by patient and physician characteristics. Diabetes is strongly linked to fatal ischemic heart disease, but its importance is underrepresented by death certificates for some subgroups.