A recently discovered stela in Guerrero represents the north-westernmost extension of monolithic sculpture in the Olmec style yet known in Mesoamerica. The stela depicts a standing human figure wearing a cloak and bird mask and holding a staff-like object. It is suggested that the theme is ceremonial or one of rank or rulership. The style of the carving and its association with Olmec style pottery confirms its colonial Olmec identity. The nature of the stela confirms our impression that Olmec presence in Guerrero and the central highlands represents more than a diffused art style. A tentative model for interpreting Olmec diffusion takes into account economic as well as socio-political factors, including possible motives bringing the Olmec into the highlands and the nature and pattern of relationships established with local culture groups. Trade and status borrowing are the basis of this model.