The recently proposed threat simulation theory (TST) states that dreaming about threatening events has a biological function. In the past few years, the TST has led to several dream content analysis studies that empirically test the theory. The predictions of the TST have been investigated mainly with a new content analysis system, the Dream Threat Scale (DTS), a method developed for identifying and classifying threatening events in dreams. In this article we review the studies that have tested the TST with the DTS. We summarize and reevaluate the results based on the dreams of Finnish and Swedish university students, traumatized and nontraumatized Kurdish, Palestinian, and Finnish children, and special dream samples, namely recurrent dreams and nightmares collected from Canadian participants. We sum up other recent research that has relevance for the TST and discuss the extent to which empirical evidence supports or conflicts with the TST. New evidence and new direct tests of the predictions of the TST yield strong support for the theory, and the TST's strengths seem to outweigh its weaknesses. © 2009 by the Board of Trustees of the University of Illinois.