Introduction: The population worldwide is rapidly ageing and demand for intensive care is increasing. People aged 85-years and over, known as the oldest old, are particularly vulnerable to critical illness due to the physiological effects of ageing. Evidence surrounding decisions to admit the oldest old to the intensive care is limited. Objective: To systematically review and synthesise published research investigating factors that influence decisions to admit the oldest old to intensive care. Methods: Systematic review and narrative synthesis. Following a comprehensive search of CINAHL, Embase and Medline databases, peer-reviewed primary research articles examining factors associated with admission or refusal to admit the oldest old to intensive care were selected. Data were extracted into tables and narratively synthesised. Results: Six studies met the inclusion criteria. Three studies identified factors associated with admission: greater pre-morbid self-sufficiency, patient preferences, alignment between the patient’s and physicians’ goals of care, age less than 85-years, and absence of cancer or previous intensive care admission. Factors associated with admission refusal were identified in all six studies and included limited bed availability, ICU physician experience, patients being deemed too ill or too well to benefit, and older age. Conclusions: Published research investigating decision-making about admission of, or refusal to admit, the oldest old to the intensive care unit is scant. The ageing population and increasing demand for intensive care resources has amplified the need for greater understanding of factors that influence intensive care admission decisions for the oldest old. Such knowledge may inform guidelines regarding complex practice and admission decisions for the oldest old, thereby ensuring their unique needs are considered and age-related disadvantage is minimised.