© 2017 Elsevier B.V. Background Bipolar patients experience sleep disturbances during and between mood episodes. Yet the impact of sleep on treatment with different medications has not been fully explored. The purpose of this paper is to explore the potential impact of poor sleep at baseline on outcomes in a randomized effectiveness trial of quetiapine and lithium. Methods The Bipolar CHOICE study was a 6-month, parallel group, multisite randomized controlled trial. Participants with bipolar disorder (N = 482; 59% female and age 18–70 years) received quetiapine or lithium. Patients were allowed to also receive adjunctive personalized treatments, which were guideline-informed, empirically-based medications added to treatment as needed. Medication changes were recorded as necessary clinical adjustments (NCA). Fisher's exact tests, mixed-regression models, and Mann-Whitney U tests were used to assess demographic and clinical characteristics as well as whether sleep disturbance would predict outcomes. Results 63% of patients had baseline sleep disturbance. Individuals with sleep disturbance had worse bipolar illness severity, greater severity of depression, mania, anxiety, irritability, and psychosis, were less likely to have sustained response (17% vs. 29%; adjusted RR: 0.55, 95% CI: 0.38–0.78, p = 0.0006) and had more NCAs (median 0.71 vs. 0.59, p = 0.03). Limitations Our findings were limited by how we defined sleep disturbance, and by how severity of sleep disturbance was assessed with one item with a non-sleep specific measure. Conclusions Baseline sleep disturbance was associated with more severe bipolar symptoms and worse 6-month outcomes. Further research is warranted on improving sleep in bipolar disorder, especially the role of psychosocial interventions.