Although sudden death has been linked to posttraumatic stress disorder (PTSD), its role in complicated grief (CG) and sudden death survivors is unknown. This questionnaire study investigated the role of peritraumatic distress in PTSD and CG symptoms in adults (n = 125) an average of 28.37 months (SD = 3.12) after a loved one's sudden death. The Peritraumatic Distress Inventory, Impact of Event Scale-Revised, and Inventory of Complicated Grief were administered to assess symptoms of peritraumatic distress, PTSD, and CG, respectively. Peritraumatic distress was the strongest correlate of both PTSD (β = .42, p < .001) and CG (β = .39, p < .001) symptoms, in a model containing current distress (Hopkins Symptom Checklist-21). Peritraumatic distress may be a key mechanism in the development of both PTSD and CG, therefore suddenly bereaved individuals reporting higher peritraumatic distress may be at risk of both adverse trauma and grief reactions.