Hepatitis B virus (HBV) infection is endemic in Taiwan, with 15-20% of the adult population carrying the surface antigen (HBsAg). Hualien in Eastern Taiwan is relatively isolated from other parts of the island by the Central Mountains. The status of HBV infection among mountain aborigines in Hualien has not been studied on a large scale before. A survey of serum HBsAg and its antibody (anti-HBs) was conducted in 1989. A total of 3,287 children from 27 primary schools in three mountainous counties of Hualien were tested. The carrier rate (HBsAg positive) for the whole group was 31.9%, and the infection rate (HBsAg and/or anti-HBs positive) was 80.7%. Both the carrier rate and infection rate of 1,618 boys were significantly higher than those of 1,669 girls (35.7% vs 28.3% and 83.0% vs 79.3%, respectively, p < 0.001). The carrier rates of children in the first to sixth grades were 29.4%, 35.0%, 31.5%, 30.8%, 33.3% and 32.0%, and the infection rates were 74.9%, 79.0%, 80.1%, 82.6%, 83.3% and 84.1%, respectively. The infection rate increased significantly with age (p < 0.05). The results show that HBV infection is a serious problem among the children of mountain aborigines in Hualien, with nearly one-third of them carrying HBsAg. Aggressive vaccination, as well as public health education programs, are greatly needed.