The decentralization process of the Health System entrusted the municipalities with responsibilities that used to be at federal level. One of these decentralized duties is the Health Surveillance for which the municipalities receive federal budget. Small municipalities struggle to meet this duty because of the lack of capacitation and the shortage of human and financial resources, producing the overlapping of duties. The aim of this research is to discuss the consequences of these duties overlapping the performance of the health surveillance role in four small municipalities in the region of Vale do Rio Caí (RS). It is both a case and a qualitative study, with data gathering through focus groups with surveillance professionals, interviews with municipal health secretaries, and consultation of municipal management documents. Data were interpreted in the content analysis perspective. Two analytical categories that explain the health surveillance functioning in these small municipalities emerged as outcomes: surveillance devaluation and lack of planning in surveillance. These outcomes enabled the critical discussion of the surveillance role in order to achieve practice comprehensiveness; the health care and management models that define health services' priorities, and the relevance of the process of decentralization and entrusting surveillance duties to small municipalities' responsibility.