DeCS - Health Sciences Descriptors The trilingual and structured vocabulary DeCS - Health Sciences Descriptors - was created by BIREME for use in indexing articles from scientific journals, books, congress proceedings, technical reports, and other types of materials, as well as for searching and retrieving subjects from scientific literature in LILACS, MEDLINE and other data bases. It was developed from the MeSH - Medical Subject Headings of the U.S. National Library of Medicine with the purpose of permitting the use of common terminology for searching in three languages, providing a consistent and unique environment for the retrieval of information regardless of the language. BIREME also developed terminology in specific areas such as Public Health, Homeopathy, Science and Health, and Health Surveillance in addition to the original MeSH terms. The concepts that characterize the DeCS vocabulary are organized in a tree structure allowing a search on broader or narrower terms or on all terms from the same tree within the hierarchical structure. DeCS is a dynamic vocabulary totaling 28,691 descriptors, of which 23,961 come from MeSH, 828 from Health Surveillance, 1,951 from Homeopathy, 3,486 from Public Health, and 218 from Science and Health. The sum is greater than the total number of descriptors, since a descriptor may occur more than once in the hierarchy. By being dynamic, it records a permanent process of change including the development of new areas of terminology. DeCS is part of the LILACS Methodology and is an integrating component of the Virtual Health Library. Its main objective is to serve as a unique language for indexing and information retrieval among the components of the Latin American and Caribbean System on Health Sciences Information, coordinated by BIREME, permitting uniform communication within approximately 600 libraries in the region. DeCS participates in the unified terminology development project, UMLS - Unified Medical Language System of the U.S. National Library of Medicine, with the responsibility of contributing with the terms in Portuguese and Spanish.