Background & Aim: Unified Medical Language System (UMLS) is an extensive ontology of biomedical knowledge developed and maintained by U.S. National Library of Medicine (NLM). Traditional Iranian Medicine (TIM) does not have any position in the structure of metathesaurus of UMLS. The main aim of this study was designing a scheme of TIM cluster's crotch mapping in the structure of metathesaurus of UMLS. Moreover, the TIM position and its proportion in the domain of vocabulary and concepts of universal medical knowledge was another aim of this study.

Materials and Methods: System analysis was the method of this study. To investigate structure of UMLS metathesaurus, and to survey lacking of TIM cluster's crotch, we applied UMLS Knowledge Source (KS) by using inductive, deductive, inductive-deductive approaches. 

Results: One Concept Unique Identifier (CUI); two synonym terms with Lexical Unique Identifier (LUI), L0025131 and L6330122; two ancestor and parent concept; nine concepts which with TIM crotch were the child concepts of two ancestor and parent; eighteen sibling concepts; six narrower; and five other related found concepts were identified for the proposal TIM crotch mapping in metathesaurus of UMLS. In addition, we found the "Biomedical Occupation or Discipline" semantic type assigned to it.

Conclusions: Current domain of metathesaurus of UMLS does not represent complete and formal domain and position of TIM. Therefore, this metathesaurus needs to depict a domain and position for TIM.