Although the possibilities of antidepressive pharmacotherapy are continuously improving, the rate of nonresponders or partial responders is still relatively high. Suicidal behavior, the most tragic consequence of untreated or unsuccessfully treated depression, commonly observed in the first few weeks of antidepressive treatment before the onset of therapeutic action, is strongly related to certain symptoms of depression like insomnia. The present paper reviews the newly discovered and well-documented antidepressive effect of quetiapine in bipolar and unipolar depression with special focus on its early onset of action and its sleep-improving effects. Both beneficial effects play an important role in the reduction of suicidal risk frequently observed in depressed patients.