From survey findings, apparently the presence of mental health problems attenuates or confounds relationships between drug use and delinquency for serious offenders and polydrug users. Although mental health problems are not strongly related to the use of drugs generally, they are apparently inversely related to problem drug use and drunk driving. Regardless of the presence or absence of mental health problems, polydrug users have the highest rates of problem drug use and drunk driving and the highest rates of self-reported delinquency. Regardless of mental-health-problem type, serious delinquents have the highest rates of alcohol, marijuana, and polydrug use, as well as the highest rates of delinquency. Overall, delinquency and drug use appear more closely related to one another than either is to mental health problems. 6 tables.