The overall aim of the thesis was to study clinical decision making in nursing. This was performed by evaluation of the quality of nurses’ diagnostic statements and comparison of the concordance between nurses and patients’ perceptions of the patients’ nursing needs, as well as patient preferences for participation in clinical decision making. Further, predictors regarding patients’ active participation were investigated. Quasi-experimental, comparative and cross-sectional descriptive study designs were used to collect data in acute care settings from randomly selected patient records (n = 140), nurse-patient dyads (n = 80), and patients discharged from hospital care (n = 428). Data were gathered using questionnaires and review of patient records. The quality of nurses’ diagnostic statements improved by the means of education directed to nurses and implementation of new forms for recording supporting nursing care planning (I). Discrepancies were found concerning patients and nurses’ perceptions about what constitutes a problem for the patient as well as the severity and importance of acting on the problem (II). Further, nurses perceived that their patients preferred to be more active in clinical decision making compared with the patients’ own preferences for participation (III). Gender, education, living situation, and occupation were identified as predictors for preferring an active role in clinical decision making (IV). The conclusions are that the accuracy of diagnostic statements needs to be addressed and validated further through systematic assessment of the patients’ perceptions and preferences concerning the health situation and preferences for participation in clinical decision making. Clinical implications are that nurses need to involve patients in identifying patient problems of relevance for nursing. Further, nurses also need to be aware of patients’ preferences for participation in clinical decision making in order that they can plan care in accordance with patient preferences and allow participation to the degree preferred by the patient