Previous research on vulnerability to Post-Traumatic Stress Disorder (PTSD) has been restricted by the absence of prospective studies that measure individual differences prior to traumatization. This study investigated the predictors of analogue post-traumatic intrusive cognitions using a fully prospective design. Non-patient participants completed a range of predictor measures before being exposed to a film about a traumatic fire. Film-induced changes in negative mood were also assessed. Subsequent intrusions were measured both within the experimental session and for a further seven days. The hypothesized predictors were: neuroticism, trait anxiety, extraversion, depression, a general tendency to suppress unpleasant thoughts, beliefs about being “at risk” from fire, mental imagery, self-rated proneness to intrusions and negative mood changes. The results showed that intrusions were predicted by film-induced increases in negative mood, thought suppression tendencies, beliefs about vulnerability to fire and self-rated proneness to intrusive cognitions. The findings are discussed in relation to the literature on thought suppression and cognitive processes in PTSD.