BACKGROUND: Perinatal obsessive-compulsive disorder (pOCD) is a common mental health difficulty. For some women with pOCD, a psychiatric in-patient admission is deemed necessary. In the UK, Mother and Baby Units (MBUs) are currently best practice for in-patient admission in the perinatal period. Wider OCD literature and pOCD case studies suggest the MBU environment may pose challenges to the treatment of pOCD. AIMS: To date, there has been no research exploring pOCD on MBUs, therefore, this study aimed to qualitatively explore women and professionals' experiences of pOCD on MBUs. METHOD: Semi-structured interviews were conducted with eight women who self-identified as having experienced pOCD and an admission to an MBU, and ten professionals who had experience working with women with pOCD on MBUs. Interviews took place virtually and were recorded and transcribed. Reflexive thematic analysis was used to analyse the data. RESULTS: Six themes were identified. (a) 'MBU a last resort for OCD', (b) 'Developing a shared understanding of OCD', (c) 'A whole team approach to treatment', (d) 'Choice and control over exposure', (e) 'Ward as a safety net' and (f) 'Transitioning back to real life'. CONCLUSIONS: The research highlighted a number of challenges in providing treatment for pOCD in this environment and suggestions are made for the development of clinical guidelines for supporting women with pOCD and designing specific training for MBU professionals.