People who use drugs in many contexts have limited access to opioid substitution therapy and HIV care. Service integration is one strategy identified to support increased access. We reviewed and synthesized literature exploring client and provider experiences of integrated opioid substitution therapy and HIV care to identify acceptable approaches to care delivery. We systematically reviewed qualitative literature. We searched nine bibliographic databases, supplemented by manual searches of reference lists of articles from the database search, relevant journals, conferences, key organizations and consultation with experts. Thematic synthesis was used to develop descriptive themes in client and provider experiences. The search yielded 11 articles for inclusion, along with 8 expert and policy reports. We identify five descriptive themes: the convenience and comprehensive nature of co-located care, contrasting care philosophies and their role in shaping integration, the limits to disclosure and communication between clients and providers, opioid substitution therapy enabling HIV care access and engagement, and health system challenges to delivering integrated services. The discussion explores how integrated opioid substitution therapy and HIV care needs to adapt to specific social conditions, rather than following universal approaches. We identify priorities for future research. Acceptable integrated opioid substitution therapy and HIV care for people who use drugs and providers is most likely through co-located care and relies upon attention to stigma, supportive relationships and client centred cultures of delivery. Further research is needed to understand experiences of integrated care, particularly delivery in low and middle income settings and models of care focused on community and non-clinic based delivery.