Objective: Cognitive-behavioral models of posttraumatic stress disorder (PTSD) propose that the content of one’s thoughts, including negative beliefs about the self, others, and world, play a fundamental role in our understanding and treatment of PTSD. Metacognitive theory suggests that metacognitive beliefs (i.e., beliefs about thinking), rather than content-specific beliefs, underlie PTSD. The present study provided the first known examination of the incremental contribution of metacognitive beliefs and trauma-related cognitions in relation to posttraumatic stress. Method: Community adults recruited through an online crowdsourcing website who reported experiencing a criterion A traumatic event (N = 299) completed self-report measures of the study variables. Results: Results from multiple linear regression analyses indicated that metacognitive beliefs of the uncontrollability and danger of thinking shared associations with each posttraumatic stress symptom cluster after accounting for the effects of content-specific beliefs and other covariates. The individual content-specific beliefs did not consistently share associations with posttraumatic stress symptoms in the regression analyses. The contribution of the individual content-specific beliefs to posttraumatic stress symptoms was consistently attenuated or rendered nonsignificant after accounting for metacognitive beliefs. Conclusions: These results are consistent with metacognitive theory in suggesting that metacognitive beliefs may be more important than trauma-related thought content in relation to posttraumatic stress.