Objectives: This study was conducted to assess the potential health impacts and improve the quality of the free immunization program in Jinju City by maximizing the predicted positive health gains and minimizing the negative health risks. Methods: A steering committee was established in September 2010 to carry out the health impact assessment (HIA) and began the screening and scoping stages. In the appraisal stage, analysis of secondary data, a literature review, case studies, geographic information systems analysis, a questionnaire, and expert consultations were used. The results of the data collection and analyses were discussed during a workshop, after which recommendations were finalized in a written report. Results: Increased access to immunization, comprehensive services provided by physicians, the strengthened role of the public health center in increasing immunization rates and services, and the ripple effect to other neighboring communities were identified as potential positive impacts. On the other hand, the program might be inaccessible to rural regions with no private clinics where there are more at-risk children, vaccine management and quality control at the clinics may be poor, and vaccines may be misused. Recommendations to maximize health gains and minimize risks were separately developed for the public health center and private clinics. Conclusions: The HIA provided an opportunity for stakeholders to comprehensively overview the potential positive and negative impacts of the program before it was implemented. An HIA is a powerful tool that should be used when developing and implementing diverse health-related policies and programs in the community.