Objective: The purpose of this study was to examine the correlation between depression levels with coping styles and cognitive errors in women treated for breast cancer. Methods: A total of 110 breast cancer outpatients who had had surgery at least 6 months previously, had completed adjuvant cancer treatment and had not experienced metastasis or recurrent lesions were evaluated. The Automatic Thoughts Questionnaire, Cognitive Errors Questionnaire, Mental Adjustment to Cancer Scale and Beck Depression Inventory were administered to all patients. Semi-structured interview forms were used to obtain medical and demographic data. All patients were categorized into depression and non-depression groups according to their Beck Depression Inventory scores. The study protocol was approved by the Medical Ethics Committee of Istanbul University Oncology Institute. Results: Higher cognitive errors and automatic thought scores were found in the depression group. Fighting spirit was found to be the primary coping style used in the non-depression group, while helplessness/hopelessness, anxious/preoccupation and fatalism were the coping styles used the most in the depression group. No association between depression and sociodemographic (except for educational level) and cancer-related variables was detected. However, it was found that automatic thoughts, cognitive errors, education level, fighting spirit and anxious/preoccupation are important indicators of depression in our sample. Conclusions: A causal relationship exists between depression and a patient's cognitive patterns and accompanying anxiety. The degree of depression is inversely related to both fighting spirit coping type and educational level. If clinicians take this into consideration, diagnosing and treating depression will be more effective.