Introduction: Contemporary ICU care enables critically ill patients to survive, however those who experience multi-organ failure and other complications now require that care for a prolonged period. It is only when we understand the total illness experience from patients’ and families’ perspectives, as well as the complexity of care for healthcare professionals that we can fully engage in developing services and promoting evidence-based practice to improve broad health outcomes and experiences for all groups. However, this range of perspectives as experienced throughout a prolonged patient ICU stay are rarely investigated in a single study. Objectives/Aims: This presentation focuses on selected findings, revealed through the use of a longitudinal design with multiple participant groups during a prolonged critical illness in the ICU. Methods: A longitudinal, qualitative, multi-case study approach was used, informed by the Chronic Illness Trajectory Framework. The trajectory concept recognises illness as a course, which can be altered by an interplay of medical, social, political, economic, biographical and psychological forces. Data collection involved six linked cases (patient, family and clinicians) in four New Zealand ICUs. Results: Longitudinal data analysis revealed four sub-phases in the trajectory of a prolonged critical illness. These sub-phases were determined by the patients’ physiological condition, with each sub-phase also representing different psychosocial needs. Families’ trajectories and nurses’ work were dominated by the patients’ trajectories with sub-phases representing different challenges for all participant groups. Conclusion: The longitudinal nature of this study with three participant groups provides a comprehensive understanding of prolonged critical illness that would never have been revealed if data collection occurred retrospectively or at a snapshot in time. Although ethically challenging, longitudinal qualitative designs reveal the interplay of factors that inform people’s experiences throughout the illness trajectory.