Internationally adopted adolescents are at increased risk for mental health problems. However, little is known about problematic alcohol and drug use, which are important indicators of maladjustment. The aim of this study was to examine the level of problematic alcohol and drug use in internationally adopted adolescents compared to their nonadopted peers. The study is based on data from the youth@hordaland-survey, which was conducted in Hordaland County, Norway, in the spring of 2012. All adolescents born from 1993 to 1995 residing in Hordaland at the time of the study were invited to participate. Information on adoption was obtained from the Central Adoption Registry and linked to self-report data from the youth@hordaland-survey. Among 10,200 participants, 45 were identified as internationally adopted. No significant differences were found between international adoptees and their peers regarding whether or not they had tried alcohol or illicit drugs or their patterns of drinking behavior. However, adopted adolescents had a higher mean score on a measure of problematic alcohol and drug use compared to their nonadopted peers. The difference was attenuated and no longer significant when adjusting for measures of depression and attention-deficit/hyperactivity disorder. Results from a structural equation model indicated a full mediation effect of mental health problems on the association between adoption status and problematic alcohol and drug use. Our findings indicate that internationally adopted adolescents experience more problematic alcohol and drug use than their nonadopted peers, and the difference can largely be explained by mental health problems.