BACKGROUND: No previous studies have investigated whether medical emergency team (MET) responses can be used to detect medical errors. OBJECTIVES: To determine whether review of MET responses can be used as a surveillance method for detecting medical errors. METHODS: Charts of all patients receiving MET responses during an 8 month period were reviewed by a hospital based Quality Improvement Committee to establish if the clinical deterioration that prompted the MET response was associated with a medical error (defined as an adverse event that was preventable with the current state of medical knowledge). Medical errors were categorized as diagnostic, treatment, or preventive errors using a descriptive typology based on previous published reports. RESULTS: Three hundred and sixty four consecutive MET responses underwent chart review and 114 (31.3%) were associated with medical errors: 77 (67.5%) were categorized as diagnostic errors, 68 (59.6%) as treatment errors, and 30 (26.3%) as prevention errors. Eighteen separate hospital care processes were identified and modified as a result of this review, 10 of which involved standardization. CONCLUSIONS: MET review may be used for surveillance to detect medical errors and to identify and modify processes of care that underlie those errors.