Objective: To evaluate the validity of death certificate diagnosis of out-of-hospital (OOH) coronary heart disease (CHD) and sudden cardiac death (SCD) in Olmsted County, Minnesota, between 1981 and 1994. Methods: In this review of the medical records, autopsy reports, and coroner's files, OOH deaths with heart disease as the underlying cause of death on the death certificate were classified into CHD (International Classification of Diseases, 9th Revision, Clinical Modification [ICD-9-CM] codes 410-414) and non-CHD (other ICD-9CM heart disease codes) deaths. A 10% random sample (n=174) of these death certificates was reviewed by physicians, and published validation criteria were applied to classify these deaths into validated CHD or non-CHD categories. Sudden cardiac death was defined as validated CHD that occurred at an OOH location with less than 24 hours between symptom onset and death. Results: The death certificate definition of OOH CHD death (ICD-9-CM codes 410-414) had high sensitivity and positive predictive value of 91% and 96%, respectively. The specificity and the negative predictive value were slightly lower at 86 % and 72%, respectively. The sensitivity of death certificate diagnosis of CHD for validated SCD was 89%, and the positive predictive value was 77%. Using a more restrictive definition of SCD, that is, less than 1 hour between the onset of symptoms and death, the positive predictive value of CHD codes for SCD was lower at 52%. Conclusions: In Olmsted County, the positive predictive values of death certificate diagnosis for OOH CHD and SCD are high. Relying on death certificate diagnoses results in about 5% underestimation of the true CHD rates, whereas their use as a surrogate for SCD yields a 16% overestimation of the true SCD rates.