What is known on the subject: If women suffer from postpartum psychosis, treatment in a specialist facility like a psychiatric mother–baby unit is recommended and should focus on the maternal health, mother–baby outcomes and the care for the next of kin. The role of mental health nurses on a mother–baby unit is essential but challenging, given the complex problems and care needs of the patient, the baby and family members. To date, very little evidence about effective nursing interventions for patients with postpartum psychosis is available. What this paper adds to existing knowledge: This paper systematically describes nursing interventions and their rationale for patients with postpartum psychosis admitted to a specialized mother–baby unit. Given the limited scientific evidence for effective nursing interventions for patients with postpartum psychosis, knowledge was obtained from a best-practice setting (i.e., a specialized mother–baby unit), thus providing a basis for the systematic development of nursing interventions to be tested on effectiveness in future studies. Implications for mental health nursing: Mental health nurses play an essential role in the multidisciplinary treatment team in providing information on the patient's personal functioning and her ability to take care for the baby, in order to determine the appropriate amount of guidance and protection, in order to prevent harm and promote recovery. To provide integrated and personalized nursing care, mental health nurses should tailor their interventions to the needs of the patient, the baby and the next of kin, adapted to the successive stages of treatment. Abstract Introduction Postpartum psychosis is one of the severest psychiatric disorders to occur in the postpartum period. If it requires a woman's admission, a psychiatric mother–baby unit is recommended, where care will focus on the mother's health, the mother–baby dyad and their next of kin. To date, few studies have examined nursing interventions for patients with postpartum psychosis. Aim Identifying nursing interventions used at a psychiatric mother–baby unit, when a patient is hospitalized with postpartum psychosis. Method A qualitative design using thematic analysis. Data were collected using semi-structured interviews (N = 13) with expert nurses working at such a unit. Results The analysis identified three themes: (a) treatment of the mental disorder, which involves interventions to improve the mother's mental and physical well-being; (b) care for the mother–baby dyad, which involves interventions intended to promote safe interactions between mother and baby; and (c) care for the partner, which involves interventions to improve the partner's well-being. Discussion Overall, within each of these themes, nurses described the urgency to tailor interventions to the needs of the patient, baby and partner. Implications to practice Our comprehensive description of interventions can be used for the improvement of nursing care for patients hospitalized with postpartum psychosis.