Users of the linked SEER-Medicare database commonly perform analyses that focus on the complex interactions among patient characteristics, cancer treatments, and outcomes. The authors review the source and scope of the patient-specific data elements, with a focus on three domains--demographic characteristics, socioeconomic characteristics, and survival status. They offer some concrete recommendations regarding the use of these data elements. In particular, they describe analyses that provide an estimate of the accuracy of the sex and age variables, and raise some cautionary notes about race and ethnicity variables. The authors describe the available measures of socioeconomic status, and recommend, with some caveats, the use of median income measures as a proxy for socioeconomic status. Finally, they describe the available data on date of death, and explain why confidence in these measures is justified.