Background: The goal of this study was to determine the characteristics that are affected in patients treated with glatiramer acetate (GA). Methods: A total of 113 patients were included in this study. Patients were treated with glatiramer acetate (subcutaneous injection, 20 mg, each day). Peripheral blood samples were obtained just prior to treatment as well as 5 years after GA treatment. All the calculations were performed with the statistical system R (r-project.org). Results: After 5 years of treatment, a significant decrease was found in the absolute and relative CD3+/CD69+ counts, the absolute and relative CD69 counts, the relative CD8+/CD38+ count and the relative CD38 count. A significant increase was found in the absolute and relative CD5+/CD45RA+ counts and the absolute CD5+/CD45RO+ count after 5 years of treatment. Conclusion: This study presents some parameters that were affected by long-term GA treatment. (C) 2018 Polish Neurological Society. Published by Elsevier Sp. z o.o. All rights reserved.