Background: Having an advance directive (AD) is associated with better care at end of life and better quality of death. However, AD completion rates among End-Stage Renal Disease patients are lower than among cancer patients. ESRD patients commonly experience cognitive impairment, reducing their ability to make their own care choices as their disease progresses. Thus, having an AD earlier in the disease trajectory is important. Little is known about differences in AD completion timing among ESRD and cancer patients. Therefore, the purpose of this study was to (1) investigate difference in AD completion and timing between ESRD and cancer patients; and, (2) identify factors associated with the early and late AD completion. Setting and Participants: A retrospective cohort study was conducted. Data was drawn from the Health and Retirement Study, a United States representative longitudinal survey of older adults, using exit interviews conducted from 2006 to 2016 among 1886 proxy reporters of deceased participants with ESRD or cancer. Results: ESRD patients had lower rates of AD completion compared to those with cancer. Higher education and being older were negatively associated with late AD completion in the last 3 months of life. Additionally, decedents with a diagnosis of ESRD, older age, and with higher education had higher odds of completing ADs one year or more before death. Discussions/Conclusions: While ESRD patient were less likely to have ADs, those that had ADS were more likely than cancer patients to develop ADs earlier in the disease trajectory. Further studies are needed to determine effective strategies to increase the AD completion rate among patients with ESRD.