analyse the conditions of use, difficulties and repercussions of different cost estimates methods in the cost-effectiveness studies of two specific technologies, vaccines against rotavirus and varicella, as well as the relationship between the cost estimates and the results. The cost estimates are conditioned by general characteristics of the disease under analysis (acute in the case of rotavirus and with long-term disability in the case of varicella), general methodological issues (theoretical choice, methods and sources of data) and specificities to the Brazilian case. This thesis brings a more detailed estimation of direct medical costs, with the inclusion of specific costs of the private health care system for the two diseases, inclusion of public participation for dispensing drugs in the case of rotavirus and inclusion of drugs costs in the public health care system in the case of varicella. As a result, there was an estimated disease total cost increase of 16% for rotavirus and 11% for varicella, as well as increase of savings (disease total cost avoided) of 18% and 16%, respectively, with the introduction of each vaccine. Although the more detailed cost estimates have reduced the incremental cost-effectiveness ratio by 20% for rotavirus and 4% for varicella, the cost-effectiveness level of the two vaccination programs was not altered. The results of the economic evaluations of vaccination against rotavirus and varicella were more sensitive to the vaccination program cost estimates, especially the vaccine price, pointing out the relevance of the cost of the technology under analysis for incorporation comparatively to the other costs. Descriptors: cost-benefit analysis; costs; vaccines; vaccines against rotavirus; vaccine against varicella Tabela 4. Análise de sensibilidade univariada, estimativas de custos e desconto, rotavírus