The impact of chronic trauma can be longstanding, affecting survivor affect regulation, consciousness, interpersonal functioning, perceptions of self and others, self-regulation, and somatic experience. There is a growing consensus that multimodal and staged approaches to treatment are necessary to promote healing. However, empirical investigations of such treatments are still needed. The current study used a naturalistic design to examine the impact of a brief, yet intensive, outpatient program on complex PTSD symptoms and attachment classification among women with histories of chronic trauma. Fifty-four women were assessed and followed over an 8-week intervention and six-month follow-up. Significant improvement over time was found for PTSD symptoms, dissociation, emotion regulation, interpersonal problems, sexual problems, alexithymia, and posttraumatic growth. Nearly, all women met criteria for PTSD at baseline, a third of the women who completed the measures no longer had PTSD post-treatment, and 60% showed a clinically significant reduction in PTSD symptoms. Finally, thirty-six women were classified as unresolved on the Adult Attachment Projective. Post-treatment, nine of 26 women who provided follow-up data were no longer classified as unresolved. Notably, those women whose attachment category changed also showed the greatest improvement in all other outcomes. Altogether, these findings suggest that an intensive, stage 1, and multimodal treatment program can benefit women with histories of chronic traumatization.