Abstract: The aim of this paper is to look at patient surveillance of “at risk” patients and how this is provided by critical care outreach services in the UK. Patient surveillance is a relatively recent development in the assessment of the seriously ill patient, within the framework of the document Critical Care Without Walls. Early recognition of potential and actual deterioration in the patient’s condition is essential, and should be accompanied by an appropriate response for early intervention. Timely access to high dependency and critical care facilities is crucial in effectively managing sick ward patients. Since the publication of Comprehensive Critical Care (2000), Early Warning Scoring systems (EWS) have been introduced onto the wards to improve the identification of patients deteriorating into critical illness. EWS tools are based upon the allocation of “points” to physiological observations, the calculation of a total ‘score’ and the designation of an agreed calling “trigger” level. Many Trusts report evidence of the benefit of track and trigger warning systems, in improving single process steps in care of the critically ill. Physiological tracking and triggering systems can lead to measurable direct and indirect improvements in the quality of patient care. Whilst supporting the development of outreach services and EWS tools, it is imperative that the future of any outreach service must be responsive to post-implementation audit and research.