Because of the widespread use of drugs by adolescents, there is demand for scientific rigor in sampling and accuracy in methods for ascertaining drug use patterns. The present study: (1) characterized adolescents who responded to advertisements for marijuana users; (2) compared rates of drug use reported on the telephone versus an on-site interview; and (3) examined drug use patterns as a function of parental awareness of drug use. Adolescents, identifying themselves as marijuana users during telephone interviews, reported more use of other drugs than those denying marijuana use. There was a high degree of correspondence between telephone and on-site interviews for all drugs except alcohol, which was reported at a higher rate on-site. Of those reporting marijuana use in the past week, 69% tested positive for marijuana in their urine-drug screens. Finally, marijuana and alcohol use patterns were higher among adolescents whose parents were aware of drug use than those whose parents indicated that their adolescent did not use marijuana. These results indicate that adolescents are willing to self-identify as marijuana users and report drug and alcohol use during telephone interviews. Additionally, parents appear to become more aware of their adolescent's drug use with increased frequency of use.