We report the results of an acute-phase and continuation-phase study of the pharmacological treatment of children and adolescents with bipolar disorders. The acute phase study, with a duration of 6-8 weeks, aimed at developing effect sizes (ES) for lithium, divalproex sodium, and carbamazepine, in the acute phase treatment of Bipolar I or II children and adolescents during a mixed or manic episode. During the acute-phase of treatment, 42 outpatients with a mean age of 11.4 yr. (20 with Bipolar I Disorder and 22 with Bipolar II Disorder) were randomly assigned to 6-8 weeks of open treatment with either lithium, divalproex sodium, or carbamazepine. The primary efficacy measures were the weekly CGI Improvement scores and the Young Mania Rating Scale. Using a ≥ 50% change from baseline to exit in the Y-MRS scores to define response, the effect size for divalproex sodium was 1.63,1.06 for lithium, and 1.00 for carbamazepine. Using this same response measure with the intent-to-treat sample, the response rates were: sodium divalproex 53%; lithium 38%; and carbamazepine 38% (x 2=0.85, 2 d.f., p=0.60). Thirty-five subjects continued in open, treatment for another 16-18 weeks, for a total of 24 weeks of prospective treatment. Overall, of the thirty-five continuation phase subjects, thirty (85%) were categorized as responders at the end of the continuation phase of treatment. Of these thirty-five subjects, 13 (37%) were only on a single mood stabilizer and no other psychotropic agents at the end of the continuation phase. Thirty-one percent of subjects in continuation were also treated with a stimulant medication in addition to mood stabilizers.