This article discusses the problem of reification ('the fallacy of misplaced concreteness'). In the psychiatric literature the reification of diagnostic categories is often mentioned as a major problem with classification systems like dsm, but the topic has received only scant attention. Possibly, this is one of the reasons why reification has persisted in psychiatry. In this article the concept is discussed in detail, together with the philosophical background. The author defines reification as the fallacy of regarding as natural kinds classification categories which are in fact artificial kinds. Finally, two common problems connected with reification in psychiatry are discussed: the tendency to engage in circular reasoning and the tendency to overestimate the importance of dsm classification.