The aim of this study was to evaluate the prevalence, severity, and management of pain in Korean patients with advanced cancer, and to identify the predictors of inadequate management of cancer pain in Korea. From 8 university hospitals, 655 patients with advanced cancer were surveyed. Information concerning analgesics prescribed was acquired from the medical records by the investigator. Physicians, nurses and caregivers were asked to estimate patients' pain. The Korean Brief Pain Inventory and the Barrier Questionnaire were completed by the patients. The Pain Management Index was estimated. Among all patients, 70.8% (464 of 655) reported pain. Among those who had pain, 63.6% (295 of 464) reported pain rated 5 or higher on a 0-10 scale. Thirty-nine percent of the patients had not received any analgesics and 53.2% were not receiving optimal pain management. Although there was a correlation between patients' pain ratings and those of doctors, nurses, and caregivers, there was no significant correlation between patients' ratings and health care providers' ratings at pain levels above moderate intensity. Cancer pain was more poorly managed in advanced cancer than terminal cancer patients (OR:3.20, 95%C.I, 1.83-5.60), in patients with better performance(OR:3.17, 95%C.I, 1.64-6.11), and in those patients whose pain was underestimated by the doctor (OR:2.58, 95%C.I. 1.42-4.69). Despite the high prevalence and severity of pain in cancer patients, the assessment and management of cancer pain were found to be inadequate in Korea.