PURPOSE: Some ICU patients remain critically ill despite reversal of the original admission diagnosis, driven by a cascade of events resulting in new and persistent organ failure. Secondary infections and systemic inflammation are important components of this cascade and may be visualised using [ METHODS: We included patients admitted to the ICU between 2017 and 2024, in whom a [ RESULTS: Forty-seven patients with persistent critical illness were included from two university medical centres. The median interval between admission and PET/CT was 21 days (IQR 14-28). In 43 patients (91%) a potential infectious or inflammatory focus was detected, of which 34 (72%) were previously unknown. The [ CONCLUSION: [