Decision making amounts to define a preorder (usually a complete one) on a set of options. Argumentation has been introduced in decision making analysis. In particular, an argument-based decision system has been proposed recently by Amgoud et al. The system is a variant of Dung’s abstract framework. It takes as input a set of options, different arguments and a defeat relation among them, and returns as outputs a status for each option, and a total preorder on the set of options. The status is defined on the basis of the acceptability of their supporting arguments. The aim of this paper is to study the revision of this decision system in light of a new argument. We will study under which conditions an option may change its status when a new argument is received and under which conditions this new argument is useless. This amounts to study how the acceptability of arguments evolves when the decision system is extended by new arguments.