Intrusions are a hallmark symptom of posttraumatic stress disorder (PTSD). While dysfunctional cognitions are known posttraumatic contributors, peritraumatic processes are less understood. Perceived threat, alongside emotional factors, is theorized as significant, but experimental studies are lacking. Using the trauma film paradigm (TFP), we investigated peritraumatic threat's impact on intrusion development. Healthy participants (N = 93) viewed different distressing film clips (low, medium, high threat). Differences among the experimental groups were examined in the frequency and distress of intrusive memories, as well as distress and expectations. As hypothesized, the frequency of intrusive memories increased with increasing threat load, as did the distress and expectations related to intrusions. Fear elicited by film clips did not mediate this effect. Perceived threat is a crucial peritraumatic factor in intrusive memory formation, suggesting that a trauma perceived as highly threatening increases intrusion likelihood. Understanding traumatic factors influencing posttraumatic symptoms helps in targeting preventive interventions.