Intrusive thoughts have been identified as key elements of chronic or traumatic stress, but many questions remain about how they operate and what causes persistence of disturbing intrusions. The present study considers these questions, examining the impact of having intrusive thoughts that are cued by stimuli in one's environment as opposed to uncued intrusions that seem to "come out of the blue." In addition, this research evaluates the extent to which distress accompanying intrusive thoughts shortly after a traumatic event predicts persistence of intrusions over time. Rescue workers who responded to the crash of Flight 427 were studied 4 to 8 weeks, and 6, 9, and 12 months after the disaster. Participants who reported crash-related thoughts that were not prompted by cues showed higher levels of distress than those reporting only cued thoughts or those reporting neither. The magnitude of distress that these thoughts caused in the first 2 months after the crash was important in predicting subsequent frequency of unwanted thoughts. The presence or absence of cues and their role in the maintenance of distress also is discussed.