In situ conservation is an effective way to conserve living organisms, particularly endangered species. One way to encourage and guarantee in situ conservation is the creation of Conservation Units. Thus, this study points out which endangered cacti are protected in these Conservation Units and which are living in unprotected areas. Furthermore, we also discuss the effectiveness of these different types of Conservation Units in protecting these endangered cacti. Initially, we made up a list of all Cactaceae species in Brazil to assign their respective extinction risk category. This list was prepared according to the ‘Flora do Brasil’ database, the IUCN Red List of Threatened Species, and the book Cacti of Eastern Brazil. We only included cacti assigned to the Near Threatened, Vulnerable, Endangered and Critically Endangered categories. We also obtained information about the phytogeographic domain and Conservation Unit where cacti grow. There are 272 species and thirty-seven genera of the Cactaceae family in Brazil. Cacti grow in all six Brazilian phytogeographic domains. We found 135 species grouped into twenty-three genera threatened with extinction in Brazil. Parodia Speg. (nineteen species), Pilosocereus Byles & Rowley (sixteen species) and Rhipsalis Gaertn. (sixteen species) are the genera with the largest number of endangered species. There is no record of endangered cacti in the Amazon Rainforest. The largest number of endangered taxa are in the Cerrado (fifty-two taxa), Caatinga (fifty-one taxa), and Atlantic Forest (forty-eight taxa). We found that about 50% of these taxa grow in unprotected areas outside Conservation Units, which means that most endangered cacti are not safe in Brazil. If we do not take urgent protection actions for their conservation, many endangered cacti will be extinct from the wild in a few years in Brazil.