A quantitative and qualitative study to identify mechanisms and actions to help harmonize cross-border health surveillance and provide a timely and effective response to events that may threaten international health security. The capacities of Brazil, Colombia, and Peru were analyzed in three areas: (a) the legal and administrative framework; (b) the ability to detect, evaluate, and report risk situations and (c) the ability to investigate, intervene in, and communicate international health risk situations. Data were collected through a document review, workshops, group work, and semistructured interviews with key individuals in health surveillance in the three countries. The average national capacity for the trio of countries within "the legal and administrative framework" was 69.4%; 83.3% in "the ability to detect, evaluate and report"; and 78.7% in "the ability to investigate, intervene in, and communicate international health risk situations." More resources should be directed toward coordinated action among the three countries in order to strengthen surveillance and public health monitoring in their border areas.