Objective: In an observer-blinded intervention trial, we tested the reduction of posttraumatic stress symptoms, aggressive attitude, and behavior in young males living in a context of ongoing community and gang violence by means of (a) forensic offender rehabilitation narrative exposure therapy (FORNET), and (b) the cognitive-behavioral intervention “Thinking for a Change” (TFAC). A waiting list served as the control condition. Method: A total of 39 young men were included in the data analysis: 15 completed FORNET, 11 underwent cognitive-behavioral therapy (CBT), and 13 were on a waiting list for later treatment. The primary efficacy endpoints were the PTSD Symptom Scale-Interview (PSS-I) severity score, the Appetitive Aggression Scale (AAS) score, and the number of perpetrated violent event types 8 months (on average) after treatment. Results: Only in the sample receiving FORNET were posttraumatic stress disorder (PTSD) scores significantly reduced at the first follow-up (Cohen’s d = −0.97) and significantly different from those of the control group (Cohen’s d = −1.03). The changes in scores for appetitive aggression and perpetrated events were not significant for any of the treatment conditions. Conclusions: The study shows that trauma-focused treatment can reduce the psychological symptoms of posttraumatic stress even for individuals living under unsafe conditions in low-income urban communities. However, achieving changes in violent behavior within a context of ongoing violence may require more than the treatment of trauma-related suffering, confrontation with one’s offenses, or cognitive-behavioral interventions.