In this paper we present a self-organizing model for open virtual environments in multi-agent based simulation systems. Open environments are inaccessible, non-deterministic, dynamic and continuous. A virtual environment is partitioned into areas called cells and is supported by an underlying autonomic software system consisting of specialized agents called controllers and coordinators. Controllers manage specific cells while coordinators monitor and guide controllers in the execution of their tasks. Controllers and coordinators continuously interact with one another and re-organize themselves and the environment structure to ensure that the simulation functional and performance requirements are met. During the execution of the simulation, virtual agents are unaware of the partitioned structure of the environment and the underlying self-organization activities. The experimental results show a significant improvement in the scalability and performance of the simulation system. Moreov...