Background: Ascertainment of vital status is critical to studies in many disease areas especially in oncology.  Two commonly used sources for mortality are SSDMF and NDI, with NDI considered the gold standard. Limitations identified in previous studies are under-ascertainment associated with the former; time lag (1-2 years) and higher cost associated with the latter. Objective: To compare ascertainment of vital status by consolidating mortality data from SSDMF and NDI vs. either source alone. Methods: Patient identifiers for a cohort of 3761 cancer patients from a large US claims database were submitted to SSDMF (cutoff February 2009) and NDI (cutoff December 2007) to obtain vital status.  Matching to SSDMF utilized SSN alone or a combination of last name, first name and birthdate. Matching to NDI utilized combinations of SSN and/or patient name, birthdate, and state of residence. For patients with a death date found in NDI, a variable indicating a true or false match was provided by NDI based on the probabilistic score. We derived the death date via a stepwise approach by utilizing all match results from either source. Results: Of 3761 patients, SSDMF returned a match for 901 (24%) patients using SSN alone, and 1088 (29%) patients using the combination.  From the NDI, 946 (25%) patients had a "true" match, 1408 (37%) had a "false" match, and remainder were considered alive.  Comparing SSDMF and NDI results utilizing both true and false NDI matches, we derived death dates for 1326 patients, which is 47% and 40% more compared to SSDMF match by SSN alone or NDI true match, respectively.  Eight patients had claims following death date and were considered false matches.  Conclusion: Utilizing all match results from SSDMF and NDI identified significantly more deceased patients compared to either source alone.  Misclassification of living patients as deceased appears minimal as verified by claims.