Purpose: An accumulation of disaster mental health research literature in the last few decades has contributed knowledge to direct disaster mental health interventions. However, no single set of principles can necessarily outline all anticipated mental health needs to be encountered in a particular disaster. Methods: To illustrate how different disaster scenarios may yield a divergence of mental health needs, this article compares mental health findings from two distinctly different studies of two very different populations affected by two very different disasters: directly exposed survivors the Oklahoma City bombing and sheltered evacuees from Hurricane Katrina. Results: Research on the two disasters reviewed illustrates many facets and complexities of postdisaster mental health needs in different populations in different settings after different types of disasters. The major findings of the Oklahoma City bombing study related to posttraumatic stress disorder and the main findings of the Hurricane Katrina study involved need for treatment of preexisting chronic mental health and substance abuse problems. Conclusion: The disaster studies in this review diverged in type of disaster, affected populations, setting, and timing of the study, and these studies yielded a divergence of findings. One disaster mental health model clearly cannot adequately describe all postdisaster scenarios. (PsycINFO Database Record (c) 2010 APA, all rights reserved)