Therapeutic use, overuse, abuse, and diversion of controlled substances in managing chronic non-cancer pain continue to be an issue for physicians and patients. The challenge is to eliminate or significantly curtail abuse of controlled prescription drugs while still assuring the proper treatment of those patients. Some physicians are apprehensive regarding the use of chronic opioid therapy in chronic non-cancer pain due to a perceived lack of proven evidence, the misuse of opioids, tolerance, dependence, and hyperalgesia. However, others have criticized the underuse of opioids, resulting in the undertreatment of pain. It has been the convention that federal, state, and local governments; professional associations; as well as pharmaceutical companies, physicians, accrediting bodies, medical licensure boards, and the public all share responsibility for preventing abuse of controlled prescription drugs. To overcome the critical challenge of eliminating or significantly curtailing abuse of controlled prescription drugs and at the same time assuring the appropriate treatment for those patients who can be helped by these medications, it is crucial to practice adherence or compliance monitoring of opioid therapy. Compliance monitoring has been shown to be crucial in delivering proper opioid therapy and preserving this therapy for the future. Urine drug testing (UDT) is considered one of the mainstays of adherence monitoring in conjunction with prescription monitoring programs and other screening tools, however, UDT is associated with multiple limitations secondary to potential pitfalls related to drug metabolism, reliability of the tests, and the knowledge of the pain physician. UDT is a widely available and familiar method for monitoring opioid use in chronic pain patients. UDT can provide tools for tracking patient compliance and expose possible drug misuse and abuse. UDT is one of the major tools of adherence monitoring in the assessment of the patient's predisposition to, and patterns of, drug misuse/abuse--a vital first step towards establishing and maintaining the safe and effective use of opioid analgesics in the treatment of chronic pain. This comprehensive review provides the role of UDT in monitoring chronic opioid therapy along with reliability and accuracy, appropriate use, overuse, misuse, and abuse.