Acute pain frequently occurs during the postoperative period. The harmful effects of pain are known and easily recognizable. The treatment of pain reduces the frequency and severity of postoperative complications, accelerates recovery, reduces days of hospitalization and reduces the possibility of development a chronic pain. It is estimated that pain is inadequately treated in the 50 % of all surgical patients. Aim: The aim of this article is to present the acute postoperative pain and its assessment and why the management of postoperative pain continues to remain problematic and insufficient. Methods: The methodology that was followed included bibliography review from both the research and the review literature of Greek and international data base which referred to assessment, management and under treatment of postoperative pain, with the use of keywords such as postoperative pain, pain management, under treatment pain, nurse's knowledge. Results: Despite medical, technologic, and pharmaceutical advancement in the past decade, inadequate management of postoperative pain remains common. Conclusions: Additional efforts are required to improve patients' postoperative pain experience. Development of new standards for pain management, pain management programs and continued education are necessary.