Inadequately controlled pain has undesirable physiologic and psychologic consequences such as increased postoperative morbidity, delayed recovery, a delayed return to normal daily living, and reduced patient satisfaction. Importantly, the lack of adequate postoperative pain treatment may lead to persistent pain after surgery, which is often overlooked. Overall, inadequate pain management increases the use of health care resources and health care costs. This article reviews the physiologic and psychologic consequences of inadequately treated pain, with an emphasis on chronic persistent postoperative pain.