The judgements made by nurses in the clinical area will determine the nursing care received by patients. Clinical judgement is, therefore, a critical aspect of professional practice. This paper outlines part of a research study that explored the influences on the clinical judgement of nurses in a mental health setting. The design used a grounded theory approach, and a number of methods were used to collect data in order to identify influences. Through the data analysis a conceptual framework of clinical judgement in mental health nursing was generated. Three inter-related concepts emerged: the self, the client and the social system in which the nurse functions. Also identified were three sub-concepts: professional roles, healthcare roles and the nurse-patient relationship. The findings of the study indicate that clinical judgements made by mental health nurses are time- and situation-dependent and consequently are unique. The implications for nursing practice, research and education are discussed, and recommendations made.