This study investigated the relationship of hyperarousal and dissociation in acute stress disorder (ASD). Civilian trauma survivors with ASD (n = 17) and without ASD (n = 15) and non-traumatized controls (n = 14) completed a hyperventilation provocation test and were administered the Beck Anxiety Inventory, the Anxiety Sensitivity Index, the Dissociative Experiences Scale, the Peritraumatic Dissociative Experiences Questionnaire, the Physical Reactions Scale, and the Agoraphobic Cognitions Questionnaire. Individuals with ASD demonstrated more panic, dissociation, and maladaptive interpretations about their arousal during the hyperventilation than non-ASD or control participants. Dissociation was associated with anxiety sensitivity and peritraumatic panic attacks. These findings suggest that hyperarousal and dissociation are highly associated in ASD and that catastrophic attributions may play a mediating role in this relationship.