Pain is the most persistent and incapacitating symptom of recurrent or metastatic cancer. About 60~90% of patients with metastatic cancer have pain long before the terminal stage of their illness. According to a recent report, in Korea, the proportion of cancer patients who have pain is 52.1% and 62.6% of them are not given adequate analgesia. Despite widespread knowledge about many aspects of pain relief and the availability of appropriate opioid analgesics, inadequate pain management in cancer patients remains pervasive. The reasons can be classified into three categories ; societal barriers, knowledge deficits, and influenced of governmental regulations. Cancer pain can be effectively treated in 85 to 95% of patients with an integrated program of systemic, pharmacologic, and anticancer therapy. However, pain relief in cancer patients remains inadequate because it is not given priority and there is a lack of education and inappropriate understanding of the nature of cancer pain. To overcome these barriers, professional education needs to be focused on the proper assessment of pain, the management of side effects, and the use of adjuvant medications. A better understanding of the pharmacology of opioid analgesics is also needed. In addition, physicians should educate patients to report pain and to take the medications prescribed for pain management effectively.