Liver histologic findings were studied in 18 children who were 4 to 9 years old, and who had been HBsAg carriers since having been infected by their mothers in the perinatal period. All were born to HBeAg-HBsAg carrier mothers; the children were followed periodically from birth. Throughout their entire course, none developed symptoms or signs suggestive of liver disease. All of the 18 children showed mild but definite liver histologic changes: 15 had nonspecific histologic changes, and three had chronic persistent hepatitis. In 13 of 18 children, follow-up aminotransferase activities were abnormal, but none exceeded 100 KU. At the time of biopsy, ALTs on four children were above the upper limit of normal. All children were HBeAg-positive in early infancy, but five lost this antigen and developed antibody during follow-up. The histologic findings in HBeAg-positive children did not differ from those in children with antibody. Perinatal hepatitis B virus infection has been thought to play an important role in chronic liver disease, including hepatocellular carcinoma. This study indicates that some pathologic changes following perinatal infection begin very early.