The paper tries to analyze the spatial definition of the Temporary Detention Centers for foreign immigrants and explores their relationships with urban context. TDCs were created in Italy in 1998, in enforcement to the Turco-Napolitano law; their original purpose was to receive and assist, for a brief period, people subjected to an expulsion measure. Yet, even if they are not part of the penitentiary circuit, these centers became more and more similar to a prison for their geographic collocation, the segregation and the control practices that characterize them. All of these aspects reveal a refusal alter, that is far from the notion of urban acceptance and that well represents a new frontier of the exclusion.