The present study replicates results of a previous pilot intervention (Sezibera et al., 2009). The objectives consist in evaluating the effectiveness of a Rumination Focused Cognitive and Behavioural Therapy (RFCBT) in treating PTSD and comorbid depression in a randomized controlled trial (RCT) conducted with young multitraumatized from the 1994 genocide against Tutsi in Rwanda. Participants (N=38) were randomly assigned to treatment group (n=19) and control group (n=19). Treatment protocol included exposure monitoring and challenging negative rumination exercises, stress management skills, and social sharing exercises. Results demonstrate significant decrease in PTSD and depression symptoms in the treatment group at posttreatment, while no changes were observed in the control group. Improvement in PTSD is a function of the improvement in rumination, social sharing and loneliness. Regarding rumination mode, decrease in analytic “WHY” thinking rumination is the best predictor of the improvement in PTSD. Depression improvement is positively associated with loneliness. The findings suggest that an intervention affecting rumination mode, lowering loneliness and increasing social sharing is with beneficial effects on PTSD and comorbid depression symptoms.