OBJECTIVE This study explored how well NANDA-I covers the reality of adult inpatient psychiatric nursing care. METHODS Patient observations documented by registered nurses in records were analyzed using content analysis and mapped with the classification NANDA-I. RESULTS A total of 1,818 notes were examined and contained 46 different patient responses. Twenty-nine patient responses were recognizable as NANDA-I diagnoses at the level of definitions, 15 as diagnoses-related factors, and 12 did not match with any NANDA-I diagnosis. CONCLUSIONS This study demonstrates that NANDA-I describes the adult inpatient psychiatric nursing care to a large extent. Nevertheless, further development of the classification is important. CONCLUSIONS The results of this study will spur nursing research and further classification development.