Intercountry adoption is increasingly common and currently involves more than 40,000 children a year in over 100 countries. Large numbers of children adopted from foreign countries are now reaching adulthood, the age of onset for most serious mental disorders, yet little is known about the effects of inter-country adoption on children's mental health. A study of children in Denmark who were adopted from abroad has found that they had a 2.9 times greater risk of developing schizophrenia than native Danes. The increased risk was independent of age at, or the region of, adoption, mental illness among foster parents, the age of foster parents or whether the foster parents lived in the city or the countryside. The foster mother's own children also had an increased (1.92 times) risk of developing schizophrenia. The researchers were not sure why this might be so but speculated that it could be due to hereditary factors in the children, traumatic experiences suffered by children prior to adoption or the disruption caused by the adoption and resettlement process itself.
Cantor-Graae, Elizabeth and Pedersen, Carsten Becker - Risk for schizophrenia in intercountry adoptees : a Danish population-based cohort study Journal of Child Psychology and Psychiatry November 2007, 48(11), 1053-1060