Online therapy offers many advantages over face-to-face therapy. Interapy includes psychoeducation, screening, effect measures, and a protocol-driven treatment via the Internet for people suffering from posttraumatic stress. The present article reports the results of a controlled trial on the Internet-driven treatment of posttraumatic stress and grief in a group of people who manifested mild to relatively severe trauma symptoms. Participants in the treatment condition (n=69) improved significantly more than participants in the waiting-list control condition (n=32) on trauma-related symptoms and general psychopathology. The effect sizes were large. On most subscales, more than 50% of the treated participants showed reliable change and clinically significant improvement, with the highest percentages being found for depression and avoidance.