In this book we seek to study the effects of Brazilian precautionary prisons, which are procedural institutes that restrict the legal good of the individual's freedom, from the perspective of protecting the citizen and society, but that such precautionary institutes fall heavily on the least favored. The object of study will be the BOM PASTOR - Female and COTEL-CENTRO DE OBSERVAÇÃO E CRIMINOLOGIA EVERARDO LUNA - Male penitentiaries and the criminal courts of the Metropolitan Region of Recife, with the aim of drawing up an etiological profile of twelve cases of prisoners with the respective reasons for the precautionary measures, and the average time spent in the prison system as a precautionary measure. The dissertation is structured in four chapters, with the central themes of the research focus delimited. We will present and address the core of the penitentiary policy exercised in the state of Pernambuco, and its model of preventive incarceration in its way of executing this precautionary detention.