One hundred ninety-five consecutive psychiatric outpatients were surveyed for covert drug abuse by a standardized technique for determining opiates, cocaine, barbiturates, and amphetamines in urine samples. On the basis of demographic variables, diagnostic information, and treatment course, patterns of abuse were defined for the 13.3 per cent with positive test results. Covert abusers demonstrated a higher incidence of adverse drug reactions and a less favorable therapy course than controls. Covert abuse was meaningfully related to misdiagnosis, management problems, and therapist’s response. Demographic variables and patient reports of previous abuse were not found to be reliable predicators of covert drug abuse. Urine screening for drug use is recommended as an aid to proper diagnosis of psychiatric outpatients that present diagnostic questions.