Aims and objectives: To identify the barriers critical care nurses experience to relative involvement in intensive care unit patient care. Background: Previous studies have discussed the experiences of relatives visiting an intensive care unit, the needs of relatives in the intensive care environment, critical care nurse and relative interaction, intensive care unit visiting policies and the benefits of including relatives in patient care. The barriers that critical care nurses experience to relative involvement in patient care have received minimal exploration. Design: Critical care nurses were recruited for a mixed methods study. An explanatory mixed method design was used, with two phases. Phase 1 was Quantitative and Phase 2 was Qualitative. Methods: Data collection occurred over five months in 2012-2013. Phase 1 used an online questionnaire (n = 70), and semi-structured interviews (n = 6) were conducted in Phase 2. Phase 1 participants were 70 critical care nurses working in Australian intensive care units and six critical care nurses were recruited from a single Sydney intensive care unit for Phase 2. Through sequential data collection, Phase 1 results formed the development of Phase 2 interview questions. Results: Participants reported various barriers to relative involvement in critically ill patient care. Factors related to the intensive care unit patient, the intensive care unit relative, the critical care nurse and the intensive care environment contributed to difficulties encompassing relative involvement. Conclusions: This study has identified that when considering relative involvement in patient care, critical care nurses take on a paternalistic role. The barriers experienced to relative involvement result in the individual critical care nurse deciding to include or exclude relatives from patient care. Relevance to clinical practice: Knowledge of the barriers to relative involvement in critically ill patient care may provide a basis for improving discussion on this topic and may assist intensive care units to implement strategies to reduce barriers.