Self-report of pain is the single most reliable indicator of pain intensity. The purpose of this study was to compare patients' and nurses' ratings of patients' pain. The sample comprised 76 patients and 65 nurses in coronary care units that rated the patient's pain intensity on a 0-10 numeric rating scale. Results showed that the mean scores of nurses were lower than their patients significantly (P < 0.01). Also, nurses assessed patients' pain intensity accurately 60% of the time. Overestimations and underestimations were 12.4% and 27.6% respectively. In addition, there were positive, moderate and significant correlations between patients' and nurses' ratings (r = 0.41, P < 0.001). Underestimation of patient's pain can have negative effects if appropriate treatment is withheld. This emphasizes the importance of a systematic assessment and acceptance of the patient's self-reported of pain.