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Background: Thymic hyperplasia presents as an anterior mediastinal mass and poses important diagnostic and therapeutic challenge. Two types of thymic hyperplasia are described: true hyperplasia and follicular hyperplasie. Literature data are peculiar concerning both entities. We aimed to describe the clinical and microscopic characteristics of thymic hyperplasia through a single institution experience during an 11-year-period., Methods: Thymic hyperplasia diagnosed during the period between 2009 and 2020 were included., Results: In all, 46 thymic hyperplasias were diagnosed. The 46 patients consisted in 33 women and 13 men with a mean age of 30 years. Microscopic diagnosis concluded to a follicular hyperplasia in 12 cases and a true thymic hyperplasia in 34 cases. The diagnosis of true thymic hyperplasia posed a diagnostic challenge with an involuted thymus in 1 case and a thymolipoma in 1 case. The confrontation with the clinical data allowed retaining the diagnosis., Conclusion: The diagnosis of thymic hyperplasia is based on microscopic features. The confrontation with clinical data and the measurements of the thymus according to the age allow to retain the diagnosis in most challenging cases., (Copyright © 2021 Elsevier Masson SAS. All rights reserved.)