At baseline, youth in the evaluated treatment group and a group in a four-session supportive comparison condition had similar demographics, past trauma exposures, and symptom severity. At follow-up, the intervention group showed significantly fewer full and partial PTSD diagnoses than the comparison group on a standardized diagnostic measure of PTSD. The intervention group had significantly lower posttraumatic and anxiety scores than the comparison group. The findings suggest that a caregiver-youth, brief preventive early intervention for youth exposed to a potentially traumatic event is a promising approach to preventing chronic PTSD. A total of 176 7 to 17-year-old youth were recruited through telephone screening based on a report of one new distressing posttraumatic stress symptom after a potentially traumatic event. Of these, 106 youth were randomly assigned to the intervention (n=53) or a 4 session supportive comparison condition (n=53). Group differences in symptom severity were assessed using repeated measures with mixed effects models of intervention group, time, and the interaction of intervention and time. Logistic regression analyses were performed in order to assess treatment condition and any subsequent exploratory chi-square analysis was performed in examining the differences in PTSD symptom criteria at follow-up. 3 tables, 2 figures, and 25 references