Background and Objective: Making advance directives or deciding on a healthcare proxy are common instruments to assure that end-of-life care is in line with one’s own wishes. Correctly specified, these instruments help health professionals and relatives to act in the best interest of the patient. We use two large population-based datasets from Germany to explore if the oldest-old (80+) make use of these instruments and what determines this use. Methods: Analyses are based on two population-based studies among persons aged 80 years and older in Germany. We perform descriptive and subsequently logistic regression analyses to identify who makes use of these instruments. In line with theoretical assumptions on healthcare behavior, we consider age, gender, education, (functional and cognitive) health, institutionalization, social embeddedness, and personal attitude (towards spirituality, assisted suicide and death) as determinants of using advance directives or deciding on a healthcare proxy. Results: The majority in both studies had either advance directives or decided on a care proxy (76.2% and 87.4%). Often participants used both (62.8%). In the large nation-wide sample, higher age, good functional health, a partnership, and a strong focus on self-determination at the end of life increased the odds of using these instruments while cognitive impairment decreased their use. In the smaller regional sample, only cognitive impairment was significantly associated with (lower) use. Conclusions: Most persons aged 80 years and older in Germany make use of advanced directives and decide on a healthcare proxy. This shows that the oldest-old want to have a say in their end-of-life care and want their alleged wishes to be considered. Persons with cognitive impairment – and thus potentially in need of these instruments – had considerably lower odds of using them. Targeted information for persons with beginning cognitive decline within the healthcare setting could thus be helpful.