Significant proportions of participants drop out of cognitive behaviour therapy for post-traumatic stress disorder (PTSD). This study indexed the pretreatment characteristics of civilian trauma survivors who remained in (n = 95) and dropped out (n = 33) of therapy for chronic PTSD. Therapy involved either cognitive behaviour therapy or supportive counselling. Participants who dropped out of therapy had higher scores on the Impact of Event Scale-Avoidance and the Catastrophic Cognitions Questionnaire, controlling for the influence of pretreatment PTSD severity. These findings suggest that retaining participants in therapy for PTSD may be enhanced by focusing initial therapy attention on modification of catastrophic cognitive styles and avoidance tendencies. (Contains 1 table.)