Although cancer elicits an array of physical and emotional symptoms, pain is often identified as the most distressing. Cancer pain may result from the primary tumor, metastasis, surgery, radiation, chemotherapy, or medical comorbidities. Although treatment with opioid analgesics is accepted as appropriate therapy for cancer-related pain, under treatment may persist among certain patients. Opioid-addicted individuals represent a challenging and heterogeneous population to treat. Addiction is linked to psychopathology and antisocial behaviors (eg, lying) which often complicate evaluation. Chronic exposure to opioids may lead to physiologic dependence and its correlates, tolerance and hyperalgesia. Given the variability and subjectivity of the cancer pain experience, there are no objective measures which capture the adequacy of pain control. Thus, when faced with complaints of uncontrolled pain, clinicians must consider a differential diagnosis of tolerance, disease progression, addiction, pseudoaddiction, chemical coping, or even criminal behavior. This article explores the cognitive, behavioral, and physiological correlates of opioid addiction that may impact cancer pain management. It also discusses risk reduction strategies for opioid misuse and research directions that may lead to improved clinical outcomes in these patients.