IntroductionLittle is known about the bone health of adults with bipolar disorder, aside from evidence purporting bone deficits among individuals with other mental illnesses, or those taking medications commonly used in bipolar disorder. In this paper, we present the methodology of a case–control study which aims to examine the role of bipolar disorder as a risk factor for bone fragility.Methods and analysisMen and women with bipolar disorder (~200 cases) will be recruited and compared with participants with no history of bipolar disorder (~1500 controls) from the Geelong Osteoporosis Study. Both cases and controls will be drawn from the Barwon Statistical Division, south-eastern Australia. The Structured Clinical Interview for DSM-IV-TR Research Version, Non-patient edition is the primary diagnostic instrument, and psychiatric symptomatology will be assessed using validated rating scales. Demographic information and detailed lifestyle data and medical history will be collected via comprehensive questionnaires. Participants will undergo dual energy X-ray absorptiometry scans and other clinical measures to determine bone and body composition. Blood samples will be provided after an overnight fast and stored for batch analysis.Ethics and disseminationEthics approval has been granted from Barwon Health Research Ethics Committee. Participation in the study is voluntary. The study findings will be disseminated via peer-reviewed publications, conference presentations and reports to the funding body.