Background: End-of-life discussions in critically-ill patients with acute surgical conditions may be rushed and occur earlier during hospitalization. This study explores the concept of sudden advanced illness (SAI) and its relevance to patients requiring Palliative and Surgical Critical Care. Methods: Semi-structured interviews were completed with 16 physicians, querying each about (1) definitional components, (2) illustrative cases, and (3) comfort with SAI. Analysis was done by grounded theory. Results: SAI was characterized as unforeseen, emerging abruptly and producing devastating injury, often in healthy, younger patients. There is (1) prognostic uncertainty, (2) loss of capacity, and (3) unprepared surrogate decision-making. Cases are emotionally-charged and often personal. Conclusion: The emerging concept of SAI is important for understanding how Palliative Care can enhance care for this subset of patients.