The urine drug screen is an important tool in adolescent medicine. Several ethical, and numerous technical, issues are associated with the use of this tool. The nature and limitations of the specific tests of which the screen is composed must be known to the physician. Two-way communication with the laboratory, both before the test is ordered and after the results are reported, can be very helpful. Laboratory testing cannot substitute for an ongoing therapeutic alliance with the patient. Testing is an important element of the substance use assessment, but is only one element, is not required in every case, and is not sufficient alone in any case.