Abstract Background Sepsis is one of the most frequent reasons for acute intensive care unit (ICU) admission of very old patients and mortality rates are high. However, the impact of pre-existing physical and cognitive function on long-term outcome of ICU patients ≥ 80 years old (very old intensive care patients (VIPs)) with sepsis is unclear. Objective To investigate both the short- and long-term mortality of VIPs admitted with sepsis and assess the relation of mortality with pre-existing physical and cognitive function. Design Prospective cohort study. Setting 241 ICUs from 22 European countries in a six-month period between May 2018 and May 2019. Subjects Acutely admitted ICU patients aged ≥80 years with sequential organ failure assessment (SOFA) score ≥ 2. Methods Sepsis was defined according to the sepsis 3.0 criteria. Patients with sepsis as an admission diagnosis were compared with other acutely admitted patients. In addition to patients’ characteristics, disease severity, information about comorbidity and polypharmacy and pre-existing physical and cognitive function were collected. Results Out of 3,596 acutely admitted VIPs with SOFA score ≥ 2, a group of 532 patients with sepsis were compared to other admissions. Predictors for 6-month mortality were age (per 5 years): Hazard ratio (HR, 1.16 (95% confidence interval (CI), 1.09–1.25, P < 0.0001), SOFA (per one-point): HR, 1.16 (95% CI, 1.14–1.17, P < 0.0001) and frailty (CFS > 4): HR, 1.34 (95% CI, 1.18–1.51, P < 0.0001). Conclusions There is substantial long-term mortality in VIPs admitted with sepsis. Frailty, age and disease severity were identified as predictors of long-term mortality in VIPs admitted with sepsis.