This article addresses the generation of traces to monitor the execution of distributed Java systems, and investigates the use of Aspect-Oriented Programming (AOP) as the instrumentation strategy to get the necessary information at runtime. The overall objective is to gather enough information to help people understand program executions by abstracting out design details related to thread and distributed communications, for instance under the form of UML sequence diagrams. We show how AspectJ, the main Java implementation of AOP, can be used to solve such issues, assuming RMI is the distribution middleware and thread communications employ specific data structures. The most important aspects are discussed and experiments on a case study are reported.