Although the direct link between child maltreatment and adult mental health outcomes is well known, the mediating role of relational factors in these associations has been underexamined. The current study aims to examine the potential mediating role of insecure attachment to romantic partners on the relationship between child maltreatment and posttraumatic stress disorder (PTSD) symptoms and posttraumatic growth (PTG). A cross-sectional study with 366 adults who have been in a romantic relationship for at least 3 months was conducted in Turkey. Data were collected through the Childhood Trauma Questionnaire Short Form, Post-Traumatic Stress Disorder Checklist-5, Posttraumatic Growth Inventory, and Experiences in Close Relationships-Revised Scale. Structural equation modeling was used to test the research hypotheses. Attachment anxiety mediated the relationship between child maltreatment and PTSD symptoms. Further, attachment avoidance mediated the relationship between child maltreatment and PTG. The findings strengthened the evidence on impaired attachment is a significant risk factor associated with psychological adjustment in adults who were maltreated as children. The findings might provide new strategies or targets for attachment-based therapeutic and preventive interventions aimed at mitigating PTSD symptoms and fostering PTG in adults who were maltreated as children.