Crustacean species from Brazil were evaluated to define their conservation status under the Categories and Criteria of the IUCN Red List of Threatened Species at the regional level. This study represents an effort of the Chico Mendes Institute for Biodiversity Conservation (ICMBio), the Brazilian agency for conservation of biodiversity, and the Brazilian Crustacean Society (SBC) to systematically collate specific data for these species and to determine their risks of extinction. The IUCN Red List Categories and Criteria were applied to 130 candidate species, following IUCN Red List Guidelines. Assessments to determine the risk of extinction were conducted during a three-day workshop held in Brasília in September 2010, which brought together about 30 experts to share information about species and threats. A total of 14 species (11.6%), 12 of them endemic to Brazil, qualified for one of the three Red List categories of threat (CR, EN, or VU). Twenty-five species (20.8%) were listed as Data Deficient, and because of this lack of data the extinction risk for crustaceans may be under-estimated. IUCN Criterion B was most often used during the assessments (85%), and the main threats identified are associated with removal of riparian forest causing siltation, and discharge of domestic, urban, industrial, and agricultural effluents, degrading water quality, as well as uncontrolled fishery activities. The South Atlantic hydrological basin contains the largest number of threatened species, which indicates that increased attention from agencies, institutions, and researchers is needed to develop appropriate strategies and regulations to aid in their conservation.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Universidade Estadual Paulista, Departamento de Ciências Biológicas, Instituto de Biociências de São Vicente