Acute pain is a symptom that represents significant concern for surgical patients during the early postoperative period. This is probably due to the use of ineffective instruments or protocols for assessment in patients with different levels of sedation after general anesthesia. This study described the relationships between the total scores obtained from two pain assessment instruments, the Non-verbal Pain Scale Revised (NVPS-R) and Critical Care Pain Observation Tool (CPOT), during the early postoperative period for non-verbal patients at Post Anesthesia Care Unit (PACU). After assessing patient’s pain with both instruments simultaneously, we determined, and evaluated the relationships between the two behavioral instruments to assess acute pain in the early postoperative period. Recent literature confirmed the research gap in assessment of postoperative pain in nonverbal patients due to inadequate evidence to guide recommendations about which specific non-verbal pain instrument to use. The results of this study present a high correlation between total pain scores of both behavioral assessment instruments, CPOT and NVPS-R, for postoperative patients after abdomino-pelvic, gastrointestinal and gynecological surgeries. Incidental findings suggest that CPOT vocalization indicator was consistently present in patients with significant pain. Increases in the NVPS-R vital signs and respiratory indicators were not seen consistently in patients with significant pain. The vital sign indicators included in the NVPS-R need to be further investigated to determine their validity for assuring pain assessment because our findings do not support their use exclusively. Physiologic indicators as heart rate, mean arterial pressure, respiratory rate and pulse oxygen saturation were not good indicators of acute pain. This study is important because pain assessment is the best way to initiate the most appropriate treatment to alleviate pain after surgery. Institutions where surgeries are performed need to standardize and provide clear policies and procedures for effective postoperative pain assessment and management. Healthcare providers are patient advocates and a clear vision in providing the most effective management contributes to decrease the worldwide problem of under treatment of acute pain.