One hundred adolescents, 12- to 18- years-old, with an acute manic episode were treated with open lithium. The response rate of the treatment was scored using the Young Mania Rating Scale and the Clinical Global Impressions Improvement scale. In addition to examining its effectiveness in reducing mania, depression, and suicidal ideation, the study also examined the potential predictors of nonresponse to the treatment, including the presence of prominent depressive features, psychosis, or psychiatric comorbidity. Exploratory analysis was also conducted to test the potential influence of early onset of mood disorders, severity of mania at initial presentation, and hospitalization on response rate. At the 4 week assessment, results revealed that 63 of the 100 subjects met response criteria, while 26 achieved remission of manic symptoms. Prominent depressive features, age at onset, severity of mania, and comorbidity did not account for the response or nonresponse of the subject to the open lithium treatment. Clinical implications of the study is that open lithium treatment appears to be effective in controlling the symptoms of acutely manic bipolar I adolescents. Future studies should examine the risks and benefits of maintenance treatment with lithium monotherapy versus combination treatment with an atypical antipsychotic agent. Tables, references