BackgroundDiabetes-related lower extremity complications such as diabetic foot ulcer (DFU) are a global disability burden. Treatment and care for patients with DFU call for a multisectoral approach that incorporates interdisciplinary care pathways. We aimed to explore the interplay between patients with DFU and healthcare professionals in cross-sectoral settings that address treatment and care and to determine “what works, for whom, and under what circumstances”.MethodThe study was designed as a realistic evaluation. The data were generated from September 2022 to March 2023 and drew upon approximately 60 h of participant observation of 14 patients during the treatment and care of DFUs in their homes (primary care) and/or at outpatient clinics (wound specialist clinics in a hospital setting) in a Danish cross-sectoral setting. The Standards for Reporting Qualitative Research (SRQR) were applied in this study.ResultsWe identified three illuminating themes that described the interplay between patients with DFU and related healthcare professionals representing both primary and secondary health care systems: (1) humour is a relationship-enhancing element between nurses and patients; (2) support from patients’ coping strategies promotes patient-centeredness and collaboration; and (3) patients and professionals occupy unnegotiated identity roles.ConclusionOur study led to a refined programme theory developed through the realistic evaluation process that allows us to propose an answer to the problem of “what works, for whom, and under what circumstances”. The interplay between patients with DFU and healthcare professionals in a cross-sectoral setting for treatment and care is characterised by the use of humour as a relation-enhancing element and by improving support for patient coping strategies, which encourages healthcare professionals to promote health literacy. Future research should examine strategies for negotiating identity roles between patients with DFU and healthcare professionals to enhance collaboration, patient health literacy, and health promotion in cross-sectoral healthcare settings.