This paper presents our work in automated mapping of medical vocabularies to the National Library of Medicine's Unified Medical Language System (UMLS). We used the UMLS Knowledge Source (KS) tool to map terms from several sources to UMLS Metathesaurus concepts. We compared performance of the KS tools with our own Minimal Representable Units Method (MRUM). The KS tools were able to map terms from 13% to 54% of the time, depending on the term set and the KS options used. Our MRUM method mapped between 96% and 99% of the terms. Based on our experience, we believe that questions remain about the best method by which the UMLS can be used to achieve automated term translation.