The prevalence of mental illness is steadily increasing, and ambulance teams frequently attend cases with suspected mental illness. A pilot project, Psychiatric Emergency Response Team (PAP), was carried out in which a prehospital emergency nurse (PEN) was accompanied by a psychiatric specialist nurse in the assessment of individuals with mental illness. The aim of the present study was to evaluate a prehospital emergency psychiatric unit from the perspective of PENs. A qualitative method using content analysis was applied. Seven senior PENs who had worked for 1 year in a prehospital psychiatric ambulance unit were interviewed individually. The analysis resulted in one main theme, “Transition from limited care and insufficient competence to improved and adequate care for psychiatric patients in ambulance care”. This emerged from six subcategories: inter-professional development, access to patient records, the ambulance vehicle, non-conveyed patients, cooperation with the police and meetings with patients and next of kin. In conclusion, these results suggest that in ambulance care in general, there is a lack of knowledge and skills about mental illnesses and initial care options. The PAP concept opened new avenues for the care of patients with mental illness, which the PENs described very positively as being helpful and valuable.