Affective disorder during pregnancy is a common and severe condition, associated with a higher risk for prenatal complications, preterm delivery, a higher rate of surgical birth and vaginal operative delivery. Depressed pregnant women are at risk for inadequate nutrition, poor weight gain, increased use of nicotine, drugs and alcohol, and failure to obtain adequate prenatal care, as well as poor mother-child attachment. Their infants have a higher risk for low birth weight, a higher rate of admission to neonatal intensive care, and cognitive, emotional and behavioural disturbances.Treatment of antepartum depression requires careful judgement to minimise risk to the foetus. Pharmacological treatment is an option, but all antidepressants cross the placenta, and both practitioners and patients are concerned about possible teratogenicity, pre- and perinatal adverse effects for the infant, as well as negative effects on long-term development. Thus, psychiatric medication use for depression in pregnancy may also pose an excess risk of preterm delivery and withdrawal symptoms in the newborn. Treatment of depression during pregnancy that is efficacious, reliable, safe, and with minor side effects is an urgent unmet clinical need. Light therapy may provide this somatic, non-pharmaceutical alternative. It is well established as the treatment of choice for Seasonal Affective Disorder (SAD), and there is a growing data base for response in nonseasonal major depression. Two promising pilot studies led to the present randomised, double-blind, placebo-controlled trial of 5 weeks daily morning bright light therapy (1h, 7000 lux white) compared with low-intensity placebo light therapy (1h, 70 lux red).