Complete and accurate ascertainment of vital status is of great importance in cohort studies. Recently, during the vital status ascertainment phase of an ongoing occupational mortality study, the authors discovered a potentially serious problem with use of the Pension Benefit Information Company's tracing service or any tracing that relies on records from the Social Security Administration (SSA) Death Master File to identify deaths. Their investigation revealed that a number of US states restrict the information in the SSA's Death Master File that is available to researchers and the public as a source of death information. As a result of these findings, the authors recommend a revised two-stage vital status tracing protocol. For stage I, data on all subjects for whom vital status is unconfirmed should be sent to the SSA. For stage II, information on all subjects to whom SSA assigned an unknown vital status as well as all subjects whom SSA identified as known decedents should be submitted to the National Death Index. This new protocol will enable researchers to maximize vital status ascertainment while containing costs associated with death identification.