Death certificates are the primary source for information used to define general mortality patterns in the United States. Analyses of mortality data generally are restricted to one of the conditions listed on the certificate--the underlying cause of dealth. We review principles related to the use of mortality data and describe a study using mortality tapes ("multiple-cause tapes") that list all conditions recorded on dealth certificates. Using multiple-cause tapes, we found that the number of deaths associated with seven infectious diseases in 1968, 1969, and 1970 was from 24% (diphtheria) to 81% (rubella) greater than that officially reported. Multiple-cause tapes also permitted a review of the association of deaths attributed to measles and varicella and known complications of these diseases. these observations confirm the usefulness of multiple-cause tapes in analyzing mortality data and emphasize the importance of examining all conditions listed on the death certificate.