Background: Depression in mothers during pregnancy and in the postnatal period has been recognized to have wide-ranging adverse impacts on offspring. Our study examines some of the outcomes and long-term economic implications experienced by offspring who have been exposed to perinatal depression. Method: We analysed the effects of perinatal depression on child development outcomes of children at ages 11 and 16 years from the community-based South London Child Development Study. Economic consequences were attached to those outcomes through simple decision-analytic techniques, building on evidence from studies of epidemiology, health-related quality of life, public sector costs and employment. The economic analysis takes a life-course perspective from the viewpoints of the public sector, individual and society. Results: Additional risks that children exposed to perinatal depression develop emotional, behavioural or cognitive problems ranged from 5% to 21%. In addition, there was a high risk (24%) that children would have special educational needs. We present results in the form of cost consequences attached to adverse child outcomes. For each child exposed to perinatal depression, public sector costs exceeded 3030, costs due to reduced earnings were 1400 and health-related quality of life loss was valued at 3760. Conclusions: Action to prevent or treat mothers’ depression during pregnancy and after birth is likely to reduce public sector costs, increase earnings and improve quality of life for children who were exposed to the condition.