The objective of this study was to analyze the representational structure of a group of users of the Unified Health System (SUS) in the city of Rio de Janeiro, Brazil, concerning the system. A qualitative research, grounded on the theory of the central nucleus of the social representations, was developed with 104 users of five health care facilities. Data were collected through the free evocation to the inducer term SUS, and analyzed by the software EVOC 2000. The structure of the representation disclosed four dimensions: conceptual, evaluative, spatial, and finalistic. They presented, respectively, the following lexicons in their central nucleus: health, well attended, hospital and attendance. Negative elements of contrast were found amidst the positive representation of the system and the presence of all four dimensions was observed in the periphery, with predominance of the finalistic one. The conclusion is that the system presents itself to the citizens in a pragmatic way and that its implementation is still necessary.