Objective-To ascertain the extent to which childhood separation anxiety disorder (SAD) confers risk for the development of psychopathology during young adulthood (ages 19-30).Method-A subset of the participants of the Oregon adolescent depression project (n = 816) was used. Subjects provided retrospective reports of lifetime mental illness (including SAD) and concurrent reports of current mental illness at age 16, and were then followed prospectively until age 30. Diagnostic assessments were conducted twice during adolescence, and again at ages 24 and 30. Based on diagnosis during childhood/adolescence, the subjects were partitioned into four orthogonal groups: SAD (n = 42), other anxiety disorders (n = 88), a heterogeneous psychiatric disorders control group (n = 389), and a not mentally ill control group (n = 297). Adjusting for demographic variables that were significantly associated with group status and for comorbid disorders prior to age 19, the results were analyzed with hierarchical multiple logistic regression.Results-SAD was a strong (78.6%) risk factor for the development of mental disorders during young adulthood. The major vulnerabilities were for panic disorder and depression.Conclusions-Because SAD creates a major vulnerability for mental disorders during young adulthood, clinicians should be sensitive to the presence of SAD, and children and adolescents with SAD should be provided with treatment. Future research should evaluate whether successful treatment for SAD and/or the provision of a preventative intervention during childhood/adolescence reduce the risk for future psychopathology.