Possibilistic description logic (PDL) is an extension of description logic based on possibilistic logic: it provides a framework to formalise knowledge allowing to encompass, model and handle uncertain information. In this paper, we consider the problem of consistency checking for PDL and propose an algorithm to compute the inconsistency degree of knowledge bases in this framework. To that aim, we present an extension of the tableau algorithm: we introduce extensions of the clash definition and completion rules to take into account the certainty associated with each formula, providing an inference procedure handling degree of certainty.