3504 patients were included in the study. 76 (2.5%) suffered an adverse event within 24 h of admission. Paramedics pre-alerted the hospital in 224 cases (7.3%). Clinical judgement demonstrated a sensitivity of 61.8% (95% CI 51.0-72.8%) with a specificity of 94.1% (95% CI 93.2-94.9%). MEWS was a good predictor of adverse outcomes and hence critical illness detection (AUC 0.799, 95% CI 0.738-0.856). Combination systems of MEWS and clinical judgement may be effective MEWS ≥4+clinical judgement: sensitivity 72