This paper presents an analysis of the cognitive component of nursing assessment, complimenting the growth in knowledge of other important aspects of assessment. The purpose of the paper is to provide a framework for understanding how nurses structure assessment problems and the types of judgements they make. The thrust of the analysis is based on a comparison between nursing assessment and medical diagnosis, since the cognitive component and judgements formed in medical diagnosis have been more fully articulated. The results suggest that there may be similarities between the cognitive strategies used in nursing assessment and those used in medical diagnosis, particularly in relation to the gathering and organization of information. But the purpose of the information search appears to be different. In medical diagnosis the aim is to establish an explanation for the patient's presenting problem. In nursing assessment, on the other hand, the aim appears to be to provide an accurate picture of the patient's current condition or situation. The assessments formulated fit the definition of a judgement and, in common with medical diagnoses, include some form of prediction. Unlike the medical diagnoses, however, which usually remain stable throughout treatment, the assessments need to change as the patient's condition changes. The cognitive component of assessment has significant implications for nurse education and clinical practice. Further understanding of how nurses structure assessment problems and formulate judgements is therefore needed. The findings may also help to clarify the meaning of nursing diagnosis.