Abstract. UML class diagrams, internationally specified and widely used in software engineering, are a great challenge in automatic drawing of graphs. Due to the complex nature of UML class diagrams and the requirements of software engineers, who need to read these diagrams, layout rules and algorithms for general graphs can not be applied without adaptions, extensions and modifications. In this paper, we present layout rules, a hierarchical layout algorithm and an edge crossing reduction strategy tailored for UML class diagrams. Furthermore, the problem of measuring aesthetic quality is discussed. 1