A cost-benefit analysis of Haemophilus influenzae type b disease preventive strategies was updated to consider evaluation of the H. influenzae type b polysaccharide-diphtheria toxoid conjugate vaccine (PRP-D) and H. influenzae type b oligosaccharide-mutant diphtheria toxin conjugate vaccine (HbOC) for children at 18 months of age. The analysis was done from the perspective of society as a whole. The economic costs of H. influenzae type b disease in the 1988 United States birth cohort would be $2.546 billion (1988 U.S. dollars) in the absence of preventive efforts. If 60% of all children could be vaccinated with PRP-D or HbOC at 18 months of age, this strategy would save $207.1 million ($88.22 savings/vaccinee; $43,605 cost/case prevented; 3.57/1 benefit-to-cost ratio) under base case model assumptions. Universal PRP-D or HbOC vaccination at 18 months of age would prevent 1845 cases of invasive H. influenzae type b disease. The break-even efficacy for universal PRP-D or HbOC vaccination at 18 months of age was 22.7%. We conclude that, under the model base case assumptions, universal PRP-D or HbOC vaccination at 18 months of age is sufficiently efficacious so that the costs of vaccination would be more than offset by decreased medical care costs for treating H. influenzae type b disease.