This study investigated patterns of mortality among a Native American tribe, the Seneca Nation of Indians (SNI). The names of 962 tribal members reported to have died in New York State between 1955 and the end of 1984 were identified through a review of tribal roll books maintained by the Seneca Nation. Positive matches were obtained for 796 (83%) of these individuals using New York State mortality files for the period under investigation. Standardized Proportionate Mortality Ratios (PMR) were computed for major causes of death based on cause-specific mortality patterns in the New York State population for each sex during the same time period. Significantly elevated risks of mortality were observed for all infectious diseases, tuberculosis, diabetes mellitus, cirrhosis, and accidents. Depressed mortality ratios were noted for deaths due to all cancers combined, and for cancers of the lung, pancreas, breast, and lymphatic/hematopoietic cancers. Changes in mortality risks over time were also observed.