Bipolar Disorder (BD) II is underdiagnosed and undertreated in postpartum women, resulting in recurrent, chronic instability of mood affecting the family, specifically the developing baby. Early diagnosis and treatment is key to the well being of the mother and baby. The objectives of this study were: 1. To test the efficacy of Quetiapine XR (dose 50-300 mg) in postpartum population; 2. To examine its safety and side effect profile in this specific population; 3. To report response and remission trends. Methods: Postpartum, non lactating patients referred to the Reproductive Mental Health Program, Vancouver, BC were included upon meeting criteria for BD II and excluded if they were psychotic/ suicidal or substance users. Eight study visits, two weeks apart were evaluated with the MINI, MADRS, HAM-D, PSQI, QLESQ, CGI and weight/ blood pressure. Visit 1 and 7 included lab tests, ie. fasting glucose, lipids, triglycerides and ECG. Results: Sixty women were screened, 20 were enrolled, and twelve completed. Recruitment continues. Dropout reasons: childcare issues/ transportation (50%), extraordinary fatigue and sedation (25%), fear of lab tests (12.5%), high levels of triglycerides(12.5%). All twelve reached remission by Visit 8, average weight loss was 1.75lbs, average dose of response was 150mg. Blood pressure remained unchanged. Conclusion: Quetiapine XR proved to be effective in the treatment of postpartum Bipolar II women. Although sedation/ somnolence was a frequent transient side effect, no major adverse events were noted. Response took place at Visit 4, with complete remission at Visit 5, with restoration to full functionality