Memories of negative emotional events persist more over time relative to memories for neutral information. Such persistence has been attributed to heightened encoding and consolidation processes. However, reactivation of the encoded information may also lead to reduced memory decay through rehearsal or a reconsolidation processes. Here, we tested whether involuntary intrusive memories, spontaneously arising following a stressful event and reactivating its memory, function to prevent memory decay, enhancing its persistence. Participants watched a stressful film containing scenes of aversive material. Memory for the film contents was tested immediately post-film using a visual recognition test. In the following five days, participants recorded intrusive memories of the film using a digitized diary. After 5-days, memory for the film contents was retested. Results indicate that in the immediate aftermath of film watching, participant's memory scores were similarly high for scenes that were later experienced as intrusions and scenes that did not intrude, suggesting effective encoding for all scenes. However, persistence of memory for scenes that intruded was preserved relative to memory for scenes that did not intrude, pointing to a mechanism through which negative intrusive memories persist over time. Implications for memory modification interventions in trauma-related psychopathology are discussed.