Patient-, physician-, and health care system-related barriers of cancer pain management in patients with malignant diseases are a recognized and widely investigated issue. The purpose of this review is to summarize the main findings of empirical research on these barriers in the literature. The most significant patient-related barriers were patient reluctance to report pain and adhere to treatment recommendations. Besides that, cognitive, affective, and sensory patient-related barriers to cancer pain management with opioid analgesics have been studied using quantitative and qualitative research methods. The Barriers Questionnaire and its shortened and modified versions were the most commonly used instruments in the context of research on patient-related barriers to cancer pain management. The most prominent physician-related barriers were insufficient physicians' knowledge about cancer pain management, inadequate patterns of pain assessment, and inadequate opioid prescription. The methodologies used to conduct the majority of the studies on physician-related barriers were weak. Nevertheless, physician knowledge of pain management guidelines, the quality of pain assessment and opioid prescription have been shown to be obviously better in a few Western countries. Institutional and health care system-related barriers were relevant only in countries with restrictive opioid prescription regulations. The evaluation of the influence of cultural-social-economical background on cancer pain management could probably help to obtain better insight into the problems of unrelieved cancer pain.