Assessing pain in critically ill patients is a challenge even in an intensive care unit (ICU) with a no sedation protocol. The aim of this study was to validate the Danish version of the pain assessment method; Critical Care Pain Observation Tool (CPOT) in an ICU with a no sedation protocol. Seventy patients were included in this study. The patients were observed during a non-nociceptive procedure (wash of an arm) and a nociceptive procedure (turning). Patients were observed before, during, and 15min after the two interventions (six assessments). Two observers participated in the data collection and CPOT scores were blinded to each other. Calculations of interrater reliability, criterion validity and discriminant validity were performed to validate the Danish version of CPOT. The results indicated a good correlation between the two raters (all scores >0.9 and P<0.05). About 48 (68.6%) of the included patients were able to self-report pain. We found a significantly higher mean CPOT score at the nociceptive procedure than at rest or the non-nociceptive procedure (P<0.05). No correlation was found between CPOT scores and physiological indicators. Patients self-reported pain and CPOT showed a significant correlation (P<0.05). A CPOT score of ≥3 correlated with patients' self-reported pain (ROC AUC 0.83). The Danish version of CPOT can be used to assess pain in critically ill patients, also when the ICU has a no sedation protocol. CPOT scores showed a good interrater reliability and correlates well with patient's self-reported pain.