Aims and objectives To detect the prevalence of NANDA‐I diagnoses and possible relationships between those and patient characteristics such as gender, age, medical diagnoses and psychiatric specialty/setting. Background There is a lack on studies about psychiatric inpatient characteristics and possible relationships among these characteristics with nursing diagnoses. Design A quantitative‐descriptive, cross‐sectional, completed data sampling study was performed. Methods The data were collected from the electronic patient record system. Frequencies for the social‐demographic data, the prevalence of the NANDA‐I diagnoses and the explanatory variables were calculated. Results In total, 410 nursing phenomena were found representing 85 different NANDA‐I diagnoses in 312 patients. The NANDA‐I diagnosis “Ineffective Coping” was the most frequently stated diagnosis followed by “Ineffective Health Maintenance,” “Hopelessness” and “Risk for Other‐Directed Violence”. Men were more frequently affected by the diagnoses “Ineffective Coping,” “Hopelessness,” “Risk for Self‐Directed Violence,” “Defensive Coping” and “Risk for Suicide,” whereas the diagnoses “Insomnia,” “Chronic Confusion,” “Chronic Low Self‐Esteem” and “Anxiety” were more common in women. Patients under the age of 45 years were more frequently affected by “Chronic Low Self‐Esteem” and “Anxiety” than older patients. “Ineffective Coping” was the most prevalent diagnosis by patients with mental disorders due to psychoactive substance use. Patients with schizophrenia were primarily affected by the diagnoses “Ineffective Coping,” “Impaired Social Interaction” and “Chronic Low Self‐Esteem.” Conclusions This study demonstrates the complexity and diversity of nursing care in inpatient psychiatric settings. Patients’ gender, age and psychiatric diagnoses and settings are a key factor for specific nursing diagnosis. Relevance to clinical practice There are tendencies for relationships between certain nursing diagnosis and patient characteristics in psychiatric adult inpatients. This enhances the specific, extended knowledge for nursing care and its demands in this setting and therefore supports the daily nursing psychiatric care and its needs.