OBJECTIVE: In part because of its cyclical nature, bipolar disorder is frequently missed or misdiagnosed in clinical practice. Over one third of bipolar patients report a period of 10+ years between initially seeking treatment and proper diagnosis. Understanding when and where bipolar disorder is being diagnosed represents an important step for targeting efforts to improve the accurate identification of bipolar patients. METHODS: To examine characteristics of initial bipolar diagnosis, the PharMetrics Integrated Outcomes Database of adjudicated medical and pharmaceutical claims for over 3 million patients from 11 U.S. health plans was utilized. We identified 3,648 bipolar patients based on the following criteria: two claims with ICD-9-CM diagnosis for bipolar disorder (296.0, 296.1, 296.4 - 296.8) that were not accompanied by a unipolar depression or schizophrenia claim on the same day, age between 10 and 64, and 1 year of continuous eligibility prior to and following the initial bipolar diagnosis. RESULTS: Of the 3648 patients, 1859 (51%) had sufficient diagnostic information to identify the current phase of the disorder. Of these 1859 patients, 69% were diagnosed during either a manic or mixed episode. Most frequently the diagnostic claim was associated with a mental health specialist (64%), with only 7% being associated with a family or general practitioner. The majority of index diagnoses were at outpatient visits (75%), followed by inpatient hospitals (15%), and Emergency Rooms (2%). On average, patients incurred $9241 in paid claims per year, of which $2610 (28%) occurred in the 2 weeks before and after the bipolar index date. During this month surrounding initial diagnosis, hospitalizations accounted for 72% of the costs. CONCLUSIONS: Bipolar disorder appears to be most commonly diagnosed at outpatient visits by mental health specialists when symptoms of mania are present. Earlier recognition and treatment may reduce the spike in costs that surrounds the initial diagnosis.