OBJECTIVES The aim of this study was to describe the 30-day mortality rate of patients aged 80 years and older undergoing surgical and nonsurgical procedures under anaesthesia in Europe and to identify risk factors associated with mortality. DESIGN A prospective cohort study. SETTING European multicentre study, performed from October 2017 to December 2018. Centres committed to a 30-day recruitment period within the study period. PATIENTS Nine thousand four hundred and ninety-seven consecutively recruited patients aged 80 years and older undergoing any kind of surgical or nonsurgical procedures under anaesthesia. MAIN OUTCOME MEASURES The primary outcome was all-cause mortality within 30 days after procedure described by Kaplan - Meier curves with 95% CI. Risk factors for 30-day mortality were analysed using a Cox regression model with 14 fixed effects and a random centre effect. RESULTS Data for 9497 patients (median age, 83.0 years; 52.8% women) from 177 academic and nonacademic hospitals in 20 countries were analysed. Patients presented with multimorbidity (77%), frailty (14%) and at least partial functional dependence (38%). The estimated 30-day mortality rate was 4.2% (95% CI 3.8 to 4.7). Among others, independent risk factors for 30-day mortality were multimorbidity, hazard ratio 1.87 (95% CI 1.26 to 2.78), frailty, hazard ratio 2.63 (95% CI 2.10 to 3.30), and limited mobility, hazard ratio 2.19 (95% CI 1.24 to 3.86). The majority of deaths (76%) occurred in hospital. Mortality risk for unplanned ICU admission was higher, hazard ratio 3.57 (95% CI 2.38 to 5.26) than for planned ICU admission, hazard ratio 1.92 (95% CI 1.47 to 2.50). Compared with other studies, the in-hospital complication rates of 17.4 and 3.9% after discharge were low. Admission to a unit with geriatric care within 30 days after the intervention was associated with a better survival within the first 10 days. CONCLUSIONS The estimated 30-day mortality rate of 4.2% was lower than expected in this vulnerable population.