AIM: To identify the relationship between one example of a rapid response system (RRS), specifically, an after-hours Clinical Team Co-Ordinator (CTC), and the incidence of Medical Emergency Team (MET) activations and, adverse and major adverse events in medical patients. METHOD: A retrospective chart audit of patients' medical records was undertaken. The intervention group consisted of 150 randomly selected medical patients admitted during three months after the introduction of the CTC after-hours service. The control group consisted of 150 randomly selected medical patients admitted before the introduction of the after-hours CTC service. Multiple logistic regression was used to determine which of the potential predictors, along with the after-hours CTC service, were associated with adverse and major adverse events. RESULTS: A total of 130 patients (n=63, 42% control; n=67, 45% intervention) exhibited physiological abnormalities that should have activated the MET yet it was only activated five times. In total there were 69 adverse events (n=32, 21% control; n=36, 25% intervention) and 25 major adverse events (n=7, 5% control; n=18, 12% intervention). There were more adverse and major adverse events identified after the introduction of the CTC after-hours service. Changes in heart rate and reduction in Glasgow Coma Scores (GCS) were significant predictors of an adverse event. A low urine output and a drop of two or more in the GCS were significant predictors of a major adverse event. CONCLUSIONS: The introduction of an after-hours CTC service in a specific clinical site was associated with an increase in the identification of adverse and major adverse events in medical patients. Further exploration of nurse-led rapid response systems should be undertaken in different clinical settings.