The purpose of this study is to identify the cue composition of clinicians' judgements for medical patients in transition states from acute to critical illness or cardiac arrest. The theoretical framework is based on Social Judgement Theory (SJT) (Hammond et al. , 1988) and the Inference/ Correspondence Model of Diagnostic Judgement (Hammond, 1996b). The clinical framework draws on a broad conceptualisation of severity of illness. The research thesis is that experienced medical ward clinicians frequently diagnose deterioration in clinical condition, and predict critical illness or cardiac arrest, using cues that are available before measurable indicators of physiological deterioration are evident. A systematic review of the research literature for the years 1990 until 2002 identified predictor cues for critical illness or cardiac arrest in general ward patients. Sixty-one papers were selected for inclusion in the review. The results indicated that objective and quantitative cues were reported most frequently. However qualitative evidence suggests subjective and perceptual cues may be used in the early recognition of deterioration (Cioffi, 2000b; Grossman & Wheeler 1997; Smith, 1988). An empirical study using qualitative interviewing of thirty-two experienced clinicians was undertaken to investigate the cue composition of nurses' judgements and the time sequence of cues reported in clinical judgements. The findings give tentative support for the research hypothesis that subjective clinician and patient self-report data are frequently the earliest cues to patient deterioration in medical patients. There was also tentative support for the hypothesis that clinicians make diagnostic, evaluative and prognostic judgements of patients' conditions in transition states from acute to critical illness or cardiac arrest. The hypothesis that diagnoses and predictions of patient condition are often reported to be accurate in critical illness, cardiac arrest or acutely ill and "vulnerable to deterioration" outcome states was examined. The hypothesis was tentatively supported in critical illness states, weakly supported in acute and vulnerable to deterioration cases, but was not supported for cardiac arrest cases. Tentative conclusions arising from the findings are as follows. The severity of the clinical state appears to differentiate patients more than their medical diagnosis. Nurses' judgements can be divided into three stages; initial, early and late with subjective and perceptual cues often the initial cues to medical patients' deterioration. Medical nurses' judgement tasks in the initial stages of clinical deterioration typically induce an intuitive form of cognition which supports the proposition of Cognitive Continuum Theory that the judgement task structure induces a corresponding type of cognition (Hammond, 1996a). A cues typology for medical patients in transition to critical illness or cardiac arrest is presented. The clinical implications of the study findings and suggestions for further research are highlighted.