Aotearoa New Zealand uses a single early warning score (EWS) across all public and private hospitals to detect adult inpatient physiological deterioration. This combines the aggregate weighted scoring of the UK National Early Warning Score with single parameter activation from Australian medical emergency team systems. We conducted a retrospective analysis of a large vital sign dataset to validate the predictive performance of the New Zealand EWS in discriminating between patients at risk of serious adverse events and compared this with the UK EWS. We also compared predictive performance for patients admitted under medical vs. surgical specialties. A total of 1,738,787 aggregate scores (13,910,296 individual vital signs) were obtained from 102,394 hospital admissions to six hospitals within the Canterbury District Health Board of New Zealand's South Island. Predictive performance of each scoring system was determined using area under the receiver operating characteristic curve. Analysis showed that the New Zealand EWS is equivalent to the UK EWS in predicting patients at risk of serious adverse events (cardiac arrest, death and/or unanticipated ICU admission). Area under the receiver operating characteristic curve for both EWSs for any adverse outcome was 0.874 (95%CI 0.871-0.878) and 0.874 (95%CI 0.870-0.877), respectively. Both EWSs showed superior predictive value for cardiac arrest and/or death in patients admitted under surgical rather than medical specialties. Our study is the first validation of the New Zealand EWS in predicting serious adverse events in a broad dataset and supports previous work showing the UK EWS has superior predictive performance in surgical rather than medical patients.