Background: This study was planned to investigate the personality traits of cancer patients in different treatment settings, and to correlate the demographics with the personality features. Materials and Methods: A total of 237 patients referred either to Marmara University School of Medicine (MUSM) Oncology Outpatient Unit or to the private office of the faculty between March 10th and April 22nd, 2010 were enrolled in the study. The Big Five Mini Test was used to evaluate the 40 personality traits of the patients. Results: The study group consisted of 98 males (41.35%) and 139 females (58.65%) with a mean age of 51. Out of the 237, 73.9% had an educational level beyond the junior high school, and 47.3% of all patients reported a positive family history for cancer. A significant difference in terms of reconcilability, extraversion, and responsibility was observed between patients admitting to the university outpatient clinic and the private office (p<0.05). Reconcilability and extraversion were found to differ between genders significantly (p<0.05). The description of the patients by him/herself or by relatives displayed a significant difference in terms of openness (p<0.05). Parameters such as educational level, family history of cancer, age and marital status showed no relevance to their characters. No discordance was observed between the self-analysis of the patient and the patient's relatives. Conclusions: Patients with cancer are typically highly reconcilable and responsible, moderately stable, open and extraverted.