Accurate knowledge of the vital status of individuals is critical to the validity of mortality research. National Death Index (NDI) and NDI-Plus are comprehensive epidemiological resources for mortality ascertainment and cause of death data that require additional user validation. Currently, there is a gap in methods to guide validation of NDI search results rendered for active duty service members. The purpose of this research was to adapt and evaluate the CDC National Program of Cancer Registries (NPCR) algorithm for mortality ascertainment in a large military cohort.