OBJECTIVE: To estimate the cost-effectiveness of introducing hepatitis B vaccine into routine infant immunization services in Mozambique, which took place in the year 2001. METHODS: A decision analytic model was used to estimate the impact of hepatitis B vaccination. This model was developed for the WHO to estimate the global burden of disease from hepatitis B. Cost data of vaccine delivery and medical treatment related to hepatitis B infection were collected for the analysis. FINDINGS: The introduction of hepatitis B vaccine has increased the annual budget for immunization services by approximately 56%. It is predicted that more than 4000 future deaths are averted annually by the intervention. In the base case scenario, the incremental costs per undiscounted deaths averted amount to US$436, and the costs per undiscounted DALY averted amount to US$36. Since the major impact of hepatitis B vaccination will not start to be evident for at least another 40 years (deaths from hepatitis B mainly occur between 40-60 years of age), the cost per DALY averted rises to US$47, when using a discount rate of 3% on health effects. We found that the monovalent hepatitis B vaccine was considerably more cost-effective than the hepatitis B vaccine in combination with DTP. INTERPRETATION: If policy makers value future health benefits equal to current benefits, the cost-effectiveness of infant hepatitis B vaccination is in the range of other primary health care interventions for which similar analysis has been undertaken.