Nine months on average after the World Trade Center (WTC) attack, 21 highly exposed adults and 10 healthy controls without major exposure did not differ in cortisol and physiologic measures. Dissociation and posttraumatic stress symptoms were quantified in the exposed group. Dissociation was associated with greater peritraumatic dissociation and, marginally, childhood trauma, lower plasma cortisol levels at 08.00h, and blunted heart rate reactivity to psychosocial stress. Posttraumatic stress was associated with exposure, peritraumatic distress, and early posttraumatic stress, and marginally associated with peritraumatic dissociation; it was not associated with cortisol or physiologic measures. Urinary cortisol differed significantly in its relationship to dissociation versus posttraumatic stress. This small study emphasizes the importance of dissecting the neurobiology of posttraumatic stress versus dissociative traumatic responses.