Objective: Quetiapine is an atypical antipsychotic with demonstrated efficacy in the treatment of adolescent schizophrenia and pediatric bipolar mania. Large, placebo-controlled studies of interventions in pediatric bipolar depression are lacking. The current study investigated the efficacy and safety of quetiapine extended-release (XR) in patients 10-17 years of age, with acute bipolar depression. Methods: This multicenter, double-blind, randomized, placebo-controlled study investigated quetiapine XR (dose range, 150-300 mg/day) in pediatric outpatients with an American Psychiatric Association, Diagnostic and Statistical Manual of Mental Disorders, 4th ed., Text Revision (DSM-IV-TR) diagnosis of bipolar I or bipolar II disorder (current or most recent episode depressed) treated for up to 8 weeks (ClinicalTrials.gov identifier: NCT00811473). The primary study outcome was mean change in Children's Depression Rating Scale-Revised (CDRS-R) total score. Secondary efficacy outcomes included CDRS-R-based response and remission rates. Results: Of 193 patients randomized to treatment, 144 patients completed the study (75.3% of quetiapine XR group [n = 70]; 74.0% of placebo group [n = 74]). Least squares mean changes in CDRS-R total score at week 8 were: -29.6 (SE, 1.65) with quetiapine XR and -27.3 (SE, 1.60) with placebo, a between-treatment group difference of -2.29 (SE, 1.99; 95% CI, -6.22, 1.65; p = 0.25; mixed-model for repeated measures analysis). Rates of response and remission did not differ significantly between treatment groups. The safety profile of quetiapine XR was broadly consistent with the profile reported previously in adult studies of quetiapine XR and pediatric studies of quetiapine immediate-release (IR). Potentially clinically significant elevations in clinical chemistry values included triglycerides (9.3%, quetiapine XR; 1.4%, placebo group) and thyroid stimulating hormone (4.7%, quetiapine XR; 0%, placebo group). An adverse event potentially related to diabetes mellitus occurred in 3.3% of the quetiapine XR versus no adverse events in the placebo group. Conclusions: Quetiapine XR did not demonstrate efficacy relative to placebo in this 8 week study of pediatric bipolar depression. Quetiapine XR was generally safe and well tolerated.