The main goal of content based image retrieval is to e ciently retrieve images that are visually similar to a query image. In this paper we will focus on content based image retrieval from large medical databases, outline the problems speci c in this area and describe the recent advances in the eld. We will also present some of the more signi cant results obtained withASSERT(AutomaticSearch and Selection Engine with Retrieval Tools), the content based image retrieval system developed in our laboratory.