Hepatitis B vaccine has been introduced into The Gambia's national Expanded Programme on Immunization, with the aim of evaluating the impact on chronic liver diseases and in particular on hepatocellular carcinoma. As part of the project, a cohort of 1000 children was recruited to assess the long-term protection induced by the vaccine. The first 3 years of follow-up are described. By the age of 3 years, 95% of the children had protective antibody levels; 4 (0.6%) are known to be carriers in contrast to the 90-140 that would be expected in the absence of vaccination. The protective effectiveness of vaccine in preventing chronic carriage in the first 3 years of life is thus estimated as 95%. Since the risk of becoming a carrier is highest in those infected early in life, these results are encouraging.