Objective: To compare the performance of mid-upper arm circumference (MUAC) against weight-for-height Z-score (WHZ) for predicting inpatient deaths in children under 5 years of age.Design: Diagnostic test accuracy study.Setting: Paediatric emergency department of a tertiary care hospital catering to semi-urban and rural population in Delhi, India.Subjects: Hospitalized children (n 1663) aged 6 months to 5 years, for whom discharge outcome was available, were consecutively recruited over 14 months. MUAC (cm), weight (kg) height (cm), clinical details and the outcome were recorded. MUAC (index test) was compared with WHZ based on the WHO growth standards (reference test) for predicting the outcome.Results: One hundred and twenty-four (7 %) children died during hospital stay. Both MUAC < 11·5 cm (adjusted OR (95 % CI): 3·7 (2·43, 5·60), P<0·001) and WHZ<-3 (2·0 (1·37, 2·99), P<0·001) served as independent predictors of inpatient mortality. However, MUAC was a significantly better predictor of mortality compared with WHZ in terms of area under the receiver-operating characteristic curve (MUAC=0·698, WHZ=0·541, P<0·001). MUAC<11·5 cm had the best trade-off of sensitivity and specificity for predicting inpatient mortality. A combination of WHZ<-3 and/or MUAC<11·5 cm did not significantly improve the predictive value over that of MUAC/WHZ, assessed individually.Conclusion: MUAC<11·5 cm is a better predictor of mortality in hospitalized under-5 children, as compared with WHZ<-3. It should be measured in all emergency settings to identify the children at higher risk of death. [ABSTRACT FROM AUTHOR]