Multilingual thesauri play a key role in multilingual text retrieval. At present, only a small number of on-line thesauri contain translations of terms in languages other than English. This is the case of the Unified Medical Language System (UMLS) Metathesaurus that includes the same term in different languages (e.g., English and Spanish). However, only a subset of terms in English have a corresponding translation in Spanish. In this work, I present an approach and some experimental results for reusing translated terms to expand the Metathesaurus. The approach includes two main tasks: finding patterns and formulating rules to automate the translation of English terms into Spanish terms. The approach is based on pattern matching, morphological rules, and word order inversion.