Individuals who are unable to communicate their pain are at greater risk for under recognition and undertreatment of pain. This position paper describes the magnitude of this issue, defines populations at risk and offers clinical practice recommendations for appropriate pain assessment using a hierarchical framework for assessing pain in those unable to self-report. Nurses have a moral, ethical, and professional obligation to advocate for all individuals in their care, particularly those who are vulnerable and unable to speak for themselves. Just like all other patients, these special populations require consistent, ongoing assessment, appropriate treatment, and evaluation of interventions to insure the best possible pain relief. Because of continued advances and new developments in strategies and tools for assessing pain in these populations, clinicians are encouraged to stay current through regular review of new research and practice recommendations.