Bipolar depression is associated with significant morbidity, high risk of suicide and substantial impairment of health-related quality of life (QOL), which adversely affects family/social relationships and occupational functioning. Depressive symptomatology is the primary determinant of quality of life, and there is a paucity of clinical trial data on how treatments affect quality of life. This 8-week, randomized, double-blind, parallel-group, placebo-controlled study in 542 patients with bipolar I or II depression used the Short Form of the Quality of Life Enjoyment and Satisfaction Questionnaire to assess the effect of quetiapine monotherapy, 300 or 600 mg/day, on quality of life. Quality of sleep was also measured using the Pittsburgh Sleep Quality Index. Both doses of quetiapine significantly improved quality of life over baseline values in comparison with placebo, which was evident at first assessment (week 4) and continued up to week 8. The improvement in quality of life was consistent over the majority of the Short Form of the Quality of Life Enjoyment and Satisfaction Questionnaire domains, and was evident in patients classified as responders on the basis of clinical efficacy measures. Quetiapine therapy also effected a significant improvement in quality of sleep compared with placebo. Improved quality of life may enhance patient compliance, and assessment of quality of life should be incorporated into future clinical trials in bipolar depression.