Context: Completion of advance directives (ADs) enhances the likelihood of receiving goal-concordant treatments near the end of life. Previous research on community samples have shown that completion of ADs is less common in lower socioeconomic status demographic group; there is a paucity of such research in patients with cancer. Objectives: To study the effect of income and education on the completion of ADs. Hypothesis: Patients with cancer having lower incomes and education levels would be less likely to report completing ADs. Methods: We conducted cross-sectional analyses of data provided by patients (n = 265) enrolled in the Values and Options in Cancer Care clinical trial. Patients with advanced cancer reported whether they had (1) completed a living will or (2) designated a health-care proxy. Response options for both questions were yes (scored 1), no (scored 0), and unsure (scored 0). We studied the association of lower household income (≤US$20 000) and education level (never attended college) with AD scores. Results: Patients with lower annual incomes had lower AD scores (estimate −0.44; confidence intervals [CI]: −0.71 to −0.16, P = .001); the association between higher educational attainment (some college or more) and completion of ADs was not statistically significant (estimate 0.04, CI: −0.16 to 0.24, P = .70). Conclusion: Interventions to promote completion of ADs among lower income patients with serious illnesses are needed.