There is limited research investigating the mechanisms underlying the lower rate of posttraumatic stress disorder (PTSD) in older compared to younger adults. This study examined age differences in peritraumatic and posttraumatic reactions, and the use of two emotion regulation strategies (rumination and positive reappraisal) using a trauma film induction paradigm. Participants (45 older adults and 45 younger adults) watched a trauma film. Eye gaze, Galvanic Skin Response, peritraumatic distress, and emotion regulation were assessed during the film. Participants completed an intrusive memory diary over the next 7 days and follow-up measures of posttraumatic symptoms and emotion regulation. Findings showed no age differences in peritraumatic distress or use of rumination or positive reappraisal during film viewing. Older adults reported lower posttraumatic stress and distress from intrusive memories than younger adults at the 1-week follow-up, despite experiencing a comparable number of intrusions. Rumination was a unique predictor of intrusive and hyperarousal symptoms, after accounting for age. There were no age differences in the use of positive appraisal, and positive reappraisal was not associated with posttraumatic stress. Lower rates of late-life PTSD may relate to decreased use of maladaptive emotion regulation (i.e., rumination), rather than increased use of adaptive emotion regulation strategies (i.e., positive reappraisal). (PsycInfo Database Record (c) 2023 APA, all rights reserved).