To evaluate Brazil's public health surveillance system (HSS), identifying its core capacities, shortcomings, and limitations in dealing with public health emergencies, within the context of the International Health Regulations (IHR 2005). In 2008-2009 an evaluative cross-sectional study was conducted using semistructured questionnaires administered to key informants (municipal, state, and national government officials) to assess Brazilian HSS structure (legal framework and resources) and surveillance and response procedures vis-à-vis compliance with the IHR (2005) requirements for management of public health emergencies of national and international concern. Evaluation criteria included the capacity to detect, assess, notify, investigate, intervene, and communicate. Responses were analyzed separately by level of government (municipal health departments, state health departments, and national Ministry of Health). Overall, at all three levels of government, Brazil's HSS has a well-established legal framework (including the essential technical regulations) and the infrastructure, supplies, materials, and mechanisms required for liaison and coordination. However, there are still some weaknesses at the state level, especially in land border areas and small towns. Professionals in the field need to be more familiar with the IHR 2005 Annex 2 decision tool (designed to increase sensitivity and consistency in the notification process). At the state and municipal level, the capacity to detect, assess, and notify is better than the capacity to investigate, intervene, and communicate. Surveillance activities are conducted 24 hours a day, 7 days a week in 40.7% of states and 35.5% of municipalities. There are shortcomings in organizational activities and methods, and in the process of hiring and training personnel. In general, the core capacities of Brazil's HSS are well established and fulfill most of the requisites listed in the IHR 2005 with respect to both structure and surveillance and response procedures, particularly at the national and state levels.