The global population is aging, with the number of ≥80-year-olds projected to triple over the next 30 years. Rates of out-of-hospital cardiac arrest (OHCA) are also increasing within this age group.The Victorian Ambulance Cardiac Arrest Registry was utilised to identify OHCAs in patients aged ≥80 years between 2002-2021. Predictors of survival to discharge were defined and a prognostic score derived from this cohort.77,628 patients experienced OHCA of whom 25,269 (32.6%) were ≥80 years (80-90 years = 18,956; 90-100 years = 6,148; >100 years = 209). The number of patients ≥80 years increased over time both absolutely (p = 0.002) and proportionally (p = 0.028). 619 (2.4%) patients survived to discharge without change over time. Older ages had no difference in witnessed OHCA status but were less likely to have shockable rhythm (OR 0.50 (95% CI 0.44-0.57) for 90-100-year-olds, OR 0.28 (95% CI 0.12-0.63) for 90-100-year-olds). If OHCA was witnessed and there was a shockable rhythm then survival was 14%; if one factor was present survival was 5-6% and if neither factor was present, survival was 0.09%. These survival rates enabled derivation of a simplified prognostic assessment score - the '15/5/0' score - highly comparable to a previously-published American cohort.Elderly OHCA rates have increased to one-third of caseload. The most important factors predicting survival were whether the OHCA was witnessed and there was a shockable rhythm. We present a simple two-point '15/5/0' prognostic score defining which patients will gain most from advanced resuscitative measures.