In this paper, we investigate the consistency issue in multi-player online games (MPOGs). Though consistency has been well-studied in parallel and distributed systems, database systems, and groupware systems, it is still a new and challenging issue for MPOGs. Most existing consistency models and consistency maintenance mechanisms adopt a data-centric approach, which is not adequate for MPOGs. We advocate a human-centric approach, and propose a consistency model based on the similarity of the perceptions of different players. The implications of the proposed consistency model in game design are also discussed. In particular, a generic consistency maintenance mechanism for MPOGs is proposed.