The NLMS is a national study of mortality over time among selected Census Bureau population samples numbering about 2.4 million. The census samples are matched to the National Death Index (NDI) maintained by the National Center for Health Statistics. The NDI is a file of all U.S. deaths since 1979 and is used to determine which individuals in the Current Population Surveys (CPS) have died. The samples are matched every other year to obtain deaths among these cohorts. Death certificates are then purchased from the states and coded for causes of death and other data. Mortality rates by age, sex, race, national origin, occupation, industry, income, education, state of residence and other factors are then obtained. The follow-up period begins with 1979, the first year covered by the NDI and ends with 1998. The total number of deaths for these cohorts is estimated to be about 250,000.