OBJECTIVES: The objective of this study was to determine the medication use patterns and costs associated with atypical antipsychotics in the treatment of bipolar disorder. METHODS: Data for this retrospective study were obtained from private payer administrative claims. Bipolar patients were identified based on one inpatient or two outpatient diagnoses of bipolar disorder. Those who initiated on olanzapine, risperidone, quetiapine, or ziprasidone during 2003, had not used the initiated medication during the prior three-months, and met eligibility criteria in prior six-months and post one-year were included. RESULTS: Among the 1516 bipolar patients in this study, olanzapine (N=507) was more likely to be initiated as the primary bipolar medication (50.9%) than risperidone (39.9%, N=424), quetiapine (36.1%, N=463) or ziprasidone (25.4%, N=122). During the post one-year, olanzapine was used as the only primary bipolar medication for more days (73.5) than risperidone (53.7), quetiapine (56.3), and ziprasidone (36.6). Overall, olanzapine and risperidone initiated patients incurred lower total annual costs ($15,208 & $14,216 respectively) than quetiapine ($18,087)and ziprasidone ($18,729) initiated patients. CONCLUSION: Among the atypical antipsychotics studied, olanzapine was used more often as a primary bipolar medication while quetiapine and ziprasidone were used more in conjunction with other bipolar medication for bipolar disorder.