Pain has been described as the 5th vital sign, and healthcare practitioners are encouraged to carefully assess pain before and after treatment. However, assessing pain in patients with disorders of consciousness or severe communication impairments is challenging. Undertreatment of pain may contribute to agitation and reduce engagement with rehabilitation therapies. Conversely, over-treatment of pain, particularly with opioid medications, can exacerbate cognitive impairments and also reduce treatment engagement. This session will define specific levels of consciousness, the brain's 'pain matrix' and will clarify how they relate to the response to nociception and to the subjective experience of pain. In addition, information on the prevalent conditions that may produce pain in this population will be presented, along with empirical data on how concerns about pain are currently being managed pharmacologically in inpatient rehabilitation settings. Existing approaches to assessing pain in patients unable to accurately report it will be summarized, and recent research on a newly developed Rasch-based observational measure of nociception and pain which permits accurate assessment in 10 - 15 minutes will be presented.