A case is presented of a 17-year-old with leukemia, pneumonia and chest-wall pain. Inadequate treatment of the patient's pain led to behavioral changes similar to those seen with idiopathic opioid psychologic dependence (addiction). The term pseudoaddiction is introduced to describe the iatrogenic syndrome of abnormal behavior developing as a direct consequence of inadequate pain management. The natural history of pseudoaddiction includes progression through 3 characteristic phases including: (1) inadequate prescription of analgesics to meet the primary pain stimulus, (2) escalation of analgesic demands by the patient associated with behavioral changes to convince others of the pain's severity, and (3) a crisis of mistrust between the patient and the health care team. Treatment strategies include establishing trust between the patient and the health care team and providing appropriate and timely analgesics to control the patient's level of pain.