The effectiveness of psychological treatments for PTSD is likely to be enhanced by improved understanding of the factors involved in maintaining the disorder. Ehlers and Clark [A cognitive model of persistent posttraumatic stem disorder Behav. Res. Ther. 38 (2000) 319-345] recently proposed a cognitive model of maintenance. The current study aimed to investigate several cognitive factors highlighted in Ehlers and Clark's model using a prospective design. Fifty-seven victims of physical or sexual assault participated in the study. Cognitive factors were assessed within 4 months of assault and victims were followed-up 6 and 9 months after the assault. Cognitive variables which significantly predicted PTSD severity at both follow-ups were: cognitive processing style during assault (mental defeat, mental confusion, detachment); appraisal of assault sequelae (appraisal of symptoms, perceived negative responses of others, permanent change); negative beliefs about self and world; and maladaptive control strategies (avoidance/safety seeking). Relationships between early appraisals, control strategies, and processing styles and subsequent PTSD severity remained significant after statistically controlling for gender and perceived assault severity. These findings support the cognitive model of PTSD proposed by Ehlers and Clark and suggest that effective treatment will need to address these cognitive factors.