Drug-addicted patients (N = 435) admitted for treatment in different clinical settings were studied. Patients were classified according to their self-report of consumed drugs and to the results of urine screening tests. Of the patients, 77.8% were active consumers, 9.6% were included in a methadone maintenance program, and 12.6% were abstinent. In the active consumer patients, positive urine screening results surpassed by far the information provided in the self-reports. Most patients tested positive to several drugs, while only 8.7% tested negative to all screened drugs. These results indicate that the information provided by drug-dependent patients lacks reliability when an analytical screening method is used simultaneously.