OBJECTIVE: The study investigated cross-sectional and longitudinal associations between bipolar disorder and other psychiatric disorders during adolescence and early adulthood. METHOD: Psychiatric interviews were administered to a representative community sample of 717 youths and their mothers in 1983 (mean age of youths=14 years) and again in 1985–1986, and 1991–1993. RESULTS: A wide range of psychiatric disorders co-occurred with bipolar disorder during adolescence and early adulthood. Adolescent anxiety disorders were uniquely associated with increased risk for early adulthood bipolar disorder after adolescent bipolar disorder was accounted for. Manic symptoms during adolescence were associated with increased risk for anxiety and depressive disorders during early adulthood after adolescent anxiety and depressive disorders were accounted for. CONCLUSIONS: Adolescents with anxiety disorders may be at increased risk for bipolar disorder or clinically significant manic symptoms during early adulthood. Adolescents with manic symptoms may be at increased risk for anxiety and depressive disorders during early adulthood.