Background Psychiatric symptoms typically cut across traditional diagnostic categories. In order to devise individually tailored treatments, there is a need to identify the basic mechanisms that underlie these symptoms. Behavioral economics provides a framework for studying these mechanisms at the behavioral level. Here, we utilized this framework to examine a widely ignored aspect of trauma‐related symptomatology—individual uncertainty attitudes—in combat veterans with and without posttraumatic stress disorder (PTSD). Methods Fifty‐seven combat veterans, including 30 with PTSD and 27 without PTSD, completed a risk and ambiguity decision‐making task that characterizes individual uncertainty attitudes, distinguishing between attitudes toward uncertain outcomes with known (“risk”) and unknown (“ambiguity”) probabilities, and between attitudes toward uncertain gains and uncertain losses. Participants’ choices were used to estimate risk and ambiguity attitudes in the gain and loss domains. Results Veterans with PTSD were more averse to ambiguity, but not risk, compared to veterans without PTSD, when making choices between possible losses, but not gains. The degree of aversion was associated with anxious arousal (e.g., hypervigilance) symptoms, as well as with the degree of combat exposure. Moreover, ambiguity attitudes fully mediated the association between combat exposure and anxious arousal symptoms. Conclusions These results provide a foundation for prospective studies of the causal association between ambiguity attitudes and trauma‐related symptoms, as well as etiologic studies of the neural underpinnings of these behavioral outcomes. More generally, these results demonstrate the potential of neuroeconomic and behavioral economic techniques for devising objective and incentive‐compatible diagnostic tools, and investigating the etiology of psychiatric disorders.