Objective: To investigate whether adding docetaxel chemotherapy to androgen deprivation therapy is effective regarding progression-free and overall survival in patients with de novo metastatic castration-sensitive prostate cancer patients with Gleason Grade Group 5 (Gleason scores 9 and 10). Study Design: Observational study. Place and Duration of the Study: Department of Medical Oncology at Manisa Celal Bayar University, Izmir Ege University, Bitlis Tatvan Public Hospital, Izmir Bozyaka Education and Research Hospital, and Izmir Kent Hospital, from March 2015 to May 2020. Methodology: Patients with de novo metastatic castration-sensitive and histopathologically confirmed GGG 5 prostate cancer were evaluated retrospectively. The patients were divided into two groups. The first group included patients who were given androgen deprivation therapy alone (ADT-only group), and the second group consisted of patients who were given ADT plus docetaxel (chemohor-monal group). The two groups were compared in terms of overall survival and progression-free survival till cut-off limit. Results: A total of 194 patients with metastatic castration-sensitive and GGG 5 prostate cancer were analysed retrospectively. The chemohormonal group comprised of 72 patients, and the ADT-only group included 122 patients. Median progression-free survival was 15.7 months in the chemohormonal group and 14.8 months in the ADT-only group (p = 0.97). The median overall survival was 37.5 months in the chemohormonal group and 37.8 months in the ADT-only group (p = 0.93). Conclusion: The addition of docetaxel chemotherapy in patients with metastatic castration-sensitive and GGG 5 prostate cancer did not result in a statistically significant difference in terms of overall survival and progression-free survival. Docetaxel may be ineffective in this group of patients.