This article takes as its initial point of focus the collaboration between the artist George Grosz and the writer Franz Jung on a publication titled Der Fall Grosz (The Grosz Case), an account of paranoia based on an actual individual, Anton Grosz, whom Jung had met in an asylum. Although the publication failed to appear in the form originally devised, it permits a rereading of the imagery of insanity that featured in Grosz's work around the time of the First World War and immediately thereafter. The argument draws connections between the pathologising of Grosz by contemporary critics and his own self-presentation as a conflicted personality. The psychoanalytic account of the mechanisms of paranoia (denial, reversal and projection) becomes blended in the discourse around Grosz with the trope of self-hatred and the article describes how this leads to the ascription of a problematic Jewish identity to him. The conclusion describes how anti-Semitism was operative within modernism and was not just a characteristic of anti-Modernist, reactionary ideologies in Germany in the early twentieth century.