It is getting harder to extract useful information from the enormous amount of data that is being collected in the medical information systems or eHealth systems due to the distributed and very complex nature of this data. Semantic web technologies, which are mainly developed for use in web information systems, are providing efficient solutions for the management of complex and distributed data, and it can be used in the medical information systems as well. Semantic web offers solutions in encoding data meaningfully, and consequently data can be searched efficiently, and integrated easily. In this paper we briefly describe semantic web technologies and present current work on the use of semantic web in medical information systems. ©2009 ACM.