OBJECTIVES: Cholesterol interacts with serotonin and it has been found to be associated with some clinical symptoms of mood disorders. There is a paucity of data on first onset bipolar patients and from Asian population. In this study, we compared the total choelsterol (TC) level between the bipolar I patients with a single manic episode (BPSM) and the normal controls, and investigated the relationship between the TC level and treatment response in the BPSM. METHODS: Twenty-five BPSM and thirty normal controls were enrolled in this study. The pretreatment and posttreatment TC levels in the BPSM were measured and comapred to that of normal controls. Young Mania Rating Scale (YMRS) was used for assessing symptom severity in the BPSM. RESULTS: The TC level was significantly lower in the BPSM than in the controls. There were negative correlations between the YMRS scores and the pretreatment TC level in the BPSM. The posttreatment TC level was significantly higher than the pretreatment TC level in the BPSM. CONCLUSION: This study suggests that the TC level can be changed after treatment in bipolar manic patients, although more studies involving different ethnic groups will be needed. Further longitudinal studies will be needed to examine the change of total cholesterol level according to the clinical course of bipolar disorder.