Objective: The evaluation of cognitive functioning is important for assessing the health of a geriatric individual. In recent years, there has been a progressive increase in the number of geriatric cancer patients. Loneliness, which is common among geriatrics, is an emotional experience that results from unmet personal or social requirements. The association between loneliness and cognitive dysfunction in elderly patients has been well-documented in the past. However, similar research has not been conducted so far in elderly cancer patients. The purpose of this study was to evaluate the impact of loneliness and cancer diagnosis on cognitive impairment in geriatric patients. Material and Methods: Elderly patients of 65 years or older were admitted to the outpatient clinics in the Department of Geriatrics and the Department of Medical Oncology for evaluation. The patients were evaluated using structured questionnaires that consisted of sociodemographic and clinical characteristics. In addition, the patients were tested with the UCLA Loneliness Scale (ULS) and the Standardized Mini-Mental State Examination (SMMSE). Results: A total of 334 geriatric patients (214 patients diagnosed with cancer, and 120 healthy/normal patients without cancer) were evaluated. Scores of ULS and SMMSE were higher in normal patients. The results of ULS and SMMSE showed a negative correlation between loneliness and cognitive functioning (r=-0.185, p=<0.001). In the multivariate analysis, neither cancer diagnosis nor loneliness was associated with cognitive impairment. Conclusion: Cancer diagnosis and loneliness were not found to be associated with cognitive impairment. The topic needs to be further studied in specific homogenous groups.