The majority of children at risk for incomplete immunizations receive care in the public sector. A multivariate model of differing health department practices and policies was developed to assess their association with immunization completion rates among health department users in Georgia's 159 county health departments. Simulations based on the model tested the impact of several programmatic and policy options. Higher immunization rates were associated with no fees, more clinical sites, computerized tracking systems, fewer missed opportunities, younger age of initial immunizations, and greater per capita budgets. A combination of these health department factors could increase immunization rates by 18 percent. © 1996 Lippincott Williams & Wilkins, Inc.