While the evidence for urine drug testing for patients on chronic opioid therapy is weak, the guidelines created by numerous medical societies and state and federal regulatory agencies recommend that it be included as one of the tools used to monitor patients for compliance with chronic opioid therapy. To get the most comprehensive results, clinicians should order both an immunoassay screen and confirmatory urine drug test. The immunoassay screen, which can be performed as an in-office point-of-care test or as a laboratory-based test, is a cheap and convenient study to order. Limitations of an immunoassay screen, however, include having a high threshold of detectability and only providing qualitative information about a select number of drug classes. Because of these restrictions, clinicians should understand that immunoassay screens have high false-positive and false-negative rates. Despite these limitations, though, the results can assist the clinician with making preliminary treatment decisions. In comparison, a confirmatory urine drug test, which can only be performed as a laboratory-based test, has a lower threshold of detectability and provides both qualitative and quantitative information. A urine drug test’s greater degree of specificity allows for a relatively low false-negative and false-positive rate in contrast to an immunoassay screen. Like any other diagnostic test, an immunoassay screen and a confirmatory urine drug test both possess limitations. Clinicians must keep this in mind when interpreting an unexpected test result and consult with their laboratory when in doubt about the meaning of the test result to avoid making erroneous decisions that negatively impact both the patient and clinician.