increase the risk of depression and anxiety with subsequent adverse effect on compliance to cancer treatment. In patients with breast cancer, childhood trauma is associated with higher levels of fatigue, stress and psychological distress and has a significant impact on patients' reaction and adjustment to cancer diagnosis. Objective: The aim of this study was to detect psychiatric comorbidity and impact of childhood trauma in patients with breast cancer and study their relations with tumor grading and histopathological characteristics. Patients and Methods: In this cross-sectional study, we recruited 150 patients diagnosed with breast cancer. Participants were females aged 18 years or older. Patients with history of another cancer, comorbid serious medical condition, in their investigation phase of cancer diagnosis or those who refused to participate in the study were excluded. The tools applied to participants were the Symptom Checklist 90 Revised and Childhood Trauma Questionnaire. Results: 113 patients (75.3%) had psychiatric comorbidity; somatization was the most common psychiatric comorbidity (58.7%) followed by depression (40.7%). Patients reported severe to extreme childhood trauma in domains of physical neglect (28%), physical abuse (22.7%), emotional neglect (7.3%), emotional abuse (18%) and sexual abuse (2%). Patients with psychiatric comorbidity had more grade III and IV in tumor grading. Patients with grade IV breast cancer had more severe psychiatric symptoms. Conclusions: Psychiatric comorbidity and childhood trauma are common in patients with breast cancer. Patients with psychiatric comorbidity have more grades III and IV tumor grading. Patients with grade IV breast cancer have more severe psychiatric symptoms.