The use of urine drug testing (UDT) has increased over recent years. UDT results have traditionally been used in legal proceedings under supervision of a medical review officer (MRO). In this context, testing has been required by statute or regulation and so is typically not in the "donor's" interest. Physicians, however, can use UDT to assist in monitoring their patient's treatment plan. By using UDT in a patient-centered fashion, both patient and physician interests are maintained. The MRO-based model of testing in the clinical setting can lead to mistrust and a deterioration of the doctor-patient relationship. Clinical testing can enhance the doctor-patient relationship when the results are used to improve communication. A patient-centered model of UDT should be used to improve quality of care. This article discusses why urine is the biological specimen of choice for drug testing; who, when and why to test; testing methods; and, most importantly, interpretation of results.