It is known that the use of classification systems in nursing care is beneficial in the context of creating and using standard language in nursing, evaluating and increasing the quality of nursing care, and creating evidence for nursing care. NANDA-I taxonomy is the most widely used in nursing. It is recommended to use NANDA-I with nursing intervention classification interventions and nursing outcomes classification indicators. Despite the many possible benefits that this system, called NNN, can provide, it is known that it is not used effectively by nurses and is believed to be complex, and therefore, its potential benefits cannot be proven. This study was carried out to explain the NNN system through the story of a case diagnosed with bipolar disorder and to set an example for the use of this system in the nursing process applied in the field of psychiatry. In addition, possible difficulties that may prevent the use of the NNN system in psychiatric nursing are discussed in the study. In this way, with the increase in the frequency of use of classification systems in practice, it will be possible to develop nursing care and to determine the effects of care on patient outcomes. The knowledge gained in this way will enable the development of evidence-based practices in nursing.Keywords: Classification systems in nursing, NANDA, NIC, NOC nursing care.