The objective of this paper is to verify the impact provoked by functional and visual barriers of gated communities on the use and security of adjacent public open spaces. Three gated communities inhabited by middle to upper income people, characterized by terraced houses and surrounded by functional and visual barriers were selected in residential neighborhoods in consolidated urban areas of Porto Alegre, Brazil. Moreover, three nearby traditional streets, characterized by visual and functional connections between public and private space, are compared with those surrounding the gated communities. The gated communities have sprawled fast around the world, and have challenged the spatial and organizational order that has shaped modern cities. The main physical and spatial characteristics, implicit in the term 'gated communities', are the physical boundaries all around, and restricted access, which eliminate the traditional interface between buildings and public open spaces, obtained through doors and windows facing the streets. Nonetheless, the impact provoked by functional and visual barriers of gated communities on the use and security of adjacent public open spaces has not been sufficiently explored. As data gathering methods were used: questionnaires, applied to 137 respondents (47 gated communities' residents and 90 neighborhoods' residents); observations of behavior; and detailed physical measurements, besides plans of the areas and the gated communities collected in public institutions. Data were statistically analyzed in SPSS/PC through nonparametric tests, and qualitatively, considering its meaning and frequency, apart from space syntax analysis of axial lines representing the streets around the gated communities. The main results confirm the existent relationship between number of functional and visual connections between the public open spaces and adjacent buildings and the use of such public open spaces. The most intensively used streets tend to be the ones characterized by higher physical permeability, whereas the least used tend to be those streets almost deprived of functional and visual connections. Moreover, results reveal a relationship between security on the streets and the number of functional and visual connections between the public open spaces and adjacent buildings. Perception of insecurity increases as the number of physical connections decreases. The negative impact caused by the visual and functional barriers of gated communities on use and security of its adjacent public open spaces, revealed by this investigation, points to the necessity of public regulation on the relationship between gated communities and its neighboring public open spaces.