Abstract: A virtual world system is an artificial environment, created inside a computer, which mimics some aspect of the real world. These systems are multiuser, allowing many people to be present and to interact simultaneously in the virtual world. The performance of virtual world systems is important because the quality of the user's experience depends on the responsiveness of the system. This paper looks at issues involved in evaluating the performance of such multiuser virtual world systems. A flexible, object-oriented framework is presented for supporting these evaluations experimentally. As an example of its usage, this framework is applied to real virtual world system and some results are presented and discussed.