AIMS AND OBJECTIVES: To report on registered nurses' situation awareness as a precursor to decision-making when recording changes in patients' conditions. BACKGROUND: Progress notes are important to communicate patients' progress and detail changes in patients' conditions. However, documentation is often poorly completed. There is little work that examines nurses' decision-making during documentation. This study focused on describing situation awareness as a precursor to decision-making during documentation. DESIGN: This study used Endsley's (Situation Awareness Analysis and Measurement, 2000, Lawrence Erlbaum Associates, NJ) work on situation awareness to guide and conceptualise information. The study was situated in a naturalistic paradigm to provide an interpretation of nurses' decision-making. METHODS: Think-aloud research methods and semi-structured interviews were employed to illuminate decision-making processes. Audio recordings and interview texts were individually examined for evidence of cues, informed by Endsley's (Situation Awareness Analysis and Measurement, 2000, Lawrence Erlbaum Associates, NJ) descriptions of situation awareness. RESULTS: As patients' conditions changed, nurses used complex mental models and pattern-matching of information, drawing on all 3 levels of situation awareness during documentation. Level 1 situation awareness provided context, level 2 situation awareness signified a change in condition and its significance for the patient, and level 3 situation awareness was evident when nurses thought aloud about what this information indicated. Three themes associated with changes in patients' conditions emerged: deterioration in condition, not responding to prescribed treatments as expected and issues related to professional practice that impacted on patients' conditions. CONCLUSION: Nurses used a complex mental model for decision-making, drawing on 3 levels of situation awareness. Hamm's cognitive continuum theory, when related to situation awareness, is a useful decision-making theory to provide a platform on which to draw together components of situation awareness and provide a framework on which to base decision-making regarding documentation. RELEVANCE TO CLINICAL PRACTICE: Understanding how RNs employ situation awareness and providing a framework for decision-making during documentation may assist effective documentation about changes in patients' conditions.