Consultation-liaison (C-L) psychiatry services aim to help general hospital staff provide better care for their patients. Recently, many inpatient C-L psychiatry services have adopted proactive and integrated approaches to achieve this aim. Despite these developments, there have been no interview-based studies of patients' and staff members' experiences of the new approaches.To gain an in-depth understanding of patients' and medical unit staff members' experiences of a proactive and integrated C-L psychiatry service for older medical inpatients (Proactive Integrated C-L Psychiatry, PICLP).We conducted an interview-based qualitative study with thematic analysis. The participants were patients and staff who had experienced PICLP during The HOME Study, a randomized trial which evaluated PICLP in 24 medical units of three UK general hospitals.We conducted 97 interviews; 43 with patients or their proxies (family members who were interviewed on behalf of patients with significant cognitive impairment) and 54 with staff members of all relevant disciplines. Patients and staff both described how PICLP was a helpful addition to medical care and discharge planning. It enhanced the medical unit team's ability to address psychological, psychiatric and social needs and provide patient-centered care. They welcomed proactive biopsychosocial assessments and the broader perspective that these offered on patients' complex problems. They also valued the integration of C-L psychiatrists into the unit teams and the daily contact with them. For patients, this fostered a therapeutic relationship and helped them to be more engaged in decisions about their medical care and discharge-planning. For staff, it enabled ready access to psychiatric expertise and training opportunities. The few reported experiences of PICLP being unhelpful were mainly about the greater number of clinicians involved in patients' care and a lack of clarity about professional roles in the integrated team.We found that older inpatients and medical unit staff experienced PICLP as both acceptable and generally helpful. Our findings add to the existing evidence for the benefits of proactive and integrated C-L psychiatry services.