Conditioning theories propose that fear of flying becomes a conditioned response through the association of flight situations with a threatening aversive event. This implicates that targeting the source of the conditioned fear is essential for exposure treatment. Therefore, the present study aims to investigate the nature of threat in fear of flying, which can be external or internal. The sample consisted of 25 undergraduate students: 12 with fear of flying and 13 controls. We measured free recall of external versus internal threat words and neutral words embedded in a dichotic listening task. The results indicated that all subjects reported more external threat words as compared to the other word categories. However, the only group difference was found for the internal threat words: subjects with fear of flying recalled significantly more internal threat words than controls. This enhanced recall for internal threat-related stimuli in individuals with fear of flying indicates that internal sensations may also be essential threat stimuli to use in exposure, next to external stimuli.