BACKGROUND: ICU survivors may experience serious psychological, physical and cognitive impairments following ICU admission, collectively termed Post Intensive Care Syndrome (PICS). Persistent pain is an underrecognized component of PICS. Previous research has shown that persistent pain is a profound clinical challenge in ICU survivors, however, research demonstrates conflicting results. Furthermore, no studies have examined the prevalence of persistent pain in ICU survivors in a contemporary Danish ICU setting. OBJECTIVES: We aim to examine the clinical trajectory, risk factors, and pathophysiology of persistent pain in ICU survivors in Denmark. DESIGN AND SAMPLE SIZE: The study is designed as a multicenter, prospective, inception cohort study with clinical follow-up. Based on the pre-study sample size calculation, 800 patients will be included. Patients will be contacted by telephone 90 days and 180 days after ICU discharge, and a series of questionnaires regarding pain, sleep quality, affective state and quality of life will be completed. A subgroup of patients will undergo a detailed clinical examination including quantitative sensory testing between 180-365 days after ICU discharge. POPULATION: Patients will be recruited from 4 Danish ICU departments. Inclusion criteria include adult patients (18 years of age), acute admission to the ICU, and an ICU admission of a minimum of 48 hours. OUTCOMES: The primary outcome is the prevalence of pain assessed by the Brief Pain Inventory (BPI) at 90 and 180 days after ICU discharge. Secondary outcomes include additional detailed descriptions of pain and daily activity, sleep quality, affective state, quality of life, treatment- and patient-related risk factors, and biomarkers associated with development of persistent pain. Substudies: \- QST substudy: 80 participants (40 with pain and 40 without pain) recruited from the main cohort will undergo Quantative Somatosensory Testing (QST). The objectives are first, to delineate somatosensory profiles of ICU survivors with and without pain, and second, to examine the presence of neuropathic pain in ICU survivors.