Abstract. In this paper, we consider the aesthetic criteria and constraints related to the layouts of UML sequence diagrams. We consider the applicability of the traditional graph drawing aesthetics in drawing sequence diagrams. Because of the special nature of sequence diagrams, many of these aesthetics are not applicable. Based on our view on how these diagrams are read or viewed, we propose some new aesthetics. We also take into account the presence of usually adopted conventions and constraints. The basic choice in producing a drawing for a sequence diagram is the linear order of the participating objects. Based on this finding and the identified aesthetics criteria, we formulate some related computational problems.