Aims and objectives: To explore the nature of relatives’ involvement in the care of patients in acute medical settings in Australia and Saudi Arabia and to explore the perceptions, attitudes and experiences of nurses. Background: There is little known about how relatives respond to being involved in patient care and the impact this has on the quality of care. Equally, little is known about how nurses enable such involvement. Previous studies have focused on settings such as critical care and paediatrics where relatives’ involvement as advocates is mostly acknowledged and accepted. Design: The study used a qualitative ethnographic approach based on an interpretive paradigm. Methods: Data collection was carried out in medical settings in two major hospitals: one in Australia and another in Saudi Arabia. Data were collected by observations and interviews over a 6-month period, with 3 months spent in each setting. Results: In both fields, relatives and nurses faced ongoing ambiguity about the role relatives should play in the hospital environment. Nurses were challenged by the unpredictability of relatives’ participation in patient care. The nurses’ fear of taking responsibility and uncertainty about the relatives’ role led them to take varied and individualised approaches to the involvement of relatives in patient care. Relatives were unclear about how to behave in the role; what the needs of patients were; and whether they were contributing positively to care and this resulted in frustration. Conclusion: The results show that ambiguity regarding the role of relatives led to problems in patient care such as safety concerns and conflict with nurses. Relevance to clinical practice: This study identified the need for patients’ relatives and nursing staff to more actively engage in negotiating and managing their respective roles in acute medical areas. This could be supported by the development and use of a set of principles or guidelines for nurses, relatives and patients regarding relatives’ involvement in hospital care settings to reduce ambiguity for all involved.