Community question answering platforms have large repositories of previously answered questions. Reusing the answers for new questions is tempting. However, not all stored answers will still be relevant. We deﬁne a new and challenging problem concerning the sustainability of questions, and present metrics aimed at distinguishing between sustainable and non-sustainable questions. We ﬁnd that an intuitive approach to sustainability of questions is not sufﬁcient, but that simple properties can already distinguish between sustainable and non-sustainable questions.