PURPOSE: The Expanded Prostate Cancer Index Composite (EPIC) is a symptom scale that measures health-related quality of life (HRQoL) in prostate cancer (PCa) patients. This scale is translated into different languages and used in daily practice. This study aimed to translate the EPIC scale into Turkish and provide Turkish validation by conducting validity and reliability analyses. METHODS: Patients with biopsy-proven PCa who received definitive or postoperative radiotherapy (RT) at our department were included. All participants were evaluated using the Turkish EPIC, The European Organization for Research and Treatment of Cancer Quality of Life Questionnaire (EORTC-QLQ) C30, and EORTC-QLQ PR25 questionnaires at five different time points. First, the original English version of the EPIC was translated into Turkish, and then, two reliability and five validity analyses were performed. RESULTS: One hundred-five patients were included in the study. In the reliability analyses, Cronbach's alpha values of the whole scale were measured at 0.866, and the main scales' Cronbach's alpha values were measured between 0.654 and 0.969. In the test-retest analysis, the correlation values of the main scales were measured between 0.413 and 0.861. The pilot study with 20 patients was completed, thus providing face validity. Sensitivity to change analysis, interscale correlation, criterion validity, and explanatory factor analyses were performed, and results proving the scale's validity were obtained in all analyses. CONCLUSION: The Turkish EPIC scale is applicable for patients in the Turkish population diagnosed with PCa who received either definitive or postoperative RT.