Cancer is increasingly prevalent in the United States, and the pain associated with it is frequently undertreated. Cancer is diagnosed in over one million Americans annually, and one of five deaths in the United States---about 1,400 per day---results from cancer. Patients with cancer often have multiple pain problems, but in most patients, the pain can be effectively controlled. Nevertheless, undertreatment is common because of a lack of knowledge by clinicians about effective assessment and management, negative attitudes of patients and clinicians toward the use of drugs for pain relief, and a variety of problems related to drug regulations, and the cost of and reimbursement for effective pain management. This guideline was developed by an interdisciplinary panel of clinicians, patients, researchers, and experts in health policy. The guideline provides a synthesis of scientific research and expert judgment to make recommendations on pain assessment and management. Approximately 470 health care professionals and 70 patients were involved either as consultants and peer reviewers or as participants in pilot testing. The Clinical Practice Guideline for the Management of Cancer Pain was commissioned by the Agency for Health Care Policy and Research (AHCPR). It follows and makes reference to an earlier guideline on acute pain management after surgery or trauma, also commissioned by AHCPR. The cancer pain guideline includes a section on the management of HIV positive/AIDS---related pain because of similarities in the sources of pain and the management approaches. This guideline is designed to help clinicians understand the assessment and treatment of cancer pain and associated symptoms. It reflects a multimodal approach to the management of pain, and it emphasizes the need for careful and continuous assessment to match interventions to the sources of pain in individual patients.