Pain management is a very important aspect in the intensive care unit (ICU), as adequate pain control has been shown to be associated with better clinical outcomes in critically ill patients. A Numerical Rating Scale (NRS) ranging from 0 to 10 (0, no pain; 10, maximum pain), which is based on a patient’s self-report, is the gold standard for pain evaluation in patients who can communicate their pain intensity. On the other hand, it is very difficult to evaluate the degree of pain in critically ill patients owing to decreased consciousness level, delirium, and the effect of sedation for mechanical ventilation management. The Behavioral Pain Scale (BPS) and Critical Care Pain Observation Tool (CPOT) have been developed for pain assessment in patients who cannot self-report their pain intensity, and recent research has confirmed their efficacy in clinical trials. In the study by Severgnini et al., published in this journal, they have demonstrated that discriminant and criterion validities of BPS and CPOT are good for the assessment of pain in mechanically ventilated critically ill patients. Besides, the authors have also shown that the combination use of these two tools is superior to the use of each tool individually. In this commentary, I would like to describe the importance and the difficulty of pain assessment in critically ill patients, discuss the validity and the reliability of the two major pain assessment tools, BPS and CPOT, and consider the future direction of pain assessment in the ICU.