96 HBsAg-positive, adopted, foreign children were followed up in an epidemiological survey aimed at evaluating the risk of spreading hepatitis B in family settings. Each year 1 400–1 900 foreign children are adopted by Swedish families, 65% of them from countries in South East Asia with a high prevalence of HBsAg-positive carriers. 92% of the HBsAg-positive children came from South East Asia and 2% from Latin America. 36/96 adopted children (37.5%) transmitted hepatitis B to 54 family members. There was a considerably greater risk of transmission by younger children. 33 children <3 years gave rise to hepatitis in 50 family members. The greatest risk of transmitting acute hepatitis B was during the first year after the arrival of the child when 22/33 cases of acute hepatitis B (67%) occurred. 65/70 children tested for HBeAg (93%) were positive. Five had anti-e antibodies and 5 converted to anti-e during follow-up.