OBJECTIVES: The aim of this study was to determine budget impact of adding Pentavalent vaccine (HIB-HBV-DTP) to the national childhood immunization schedule in Iran.  METHODS:  An excel-based model was developed to determine the costs of including Pentavalent vaccine to the program, comparing present schedule to previous one (including separate DTP and Hepatitis B vaccines). Total annual costs included cost of vaccination (vaccine and syringe) and cost of Haemophilus influenzae type b (Hib) diseases treatment from the perspective of the government. The health outcomes were considered as estimated annual Hib diseases cases. The net budget impact was the difference of total annual costs in two schedules. RESULTS:  The total cost of vaccination during 5 years is US$18,060,463 in previous program and US$67,774,786 in present program, inclusion of Pentavalent vaccine increases the vaccination costs about 49 million dollars, but saves approximately 6 million dollars in healthcare costs. During 5 years of immunization, the incremental cost to the government is about 43 million dollars. CONCLUSIONS:  The arrival of the Pentavalent vaccine increases the financial burden to the government. Economic evaluation studies (cost-effectiveness and budget impact analysis) can help determine the appropriate and reasonable prices for vaccines and reduce the budget impact.