The condition of true thymic hyperplasia is defined as an increase of both size and weight of the gland while it maintains normal microscopic architecture. It occurs in three different clinicopathologic forms: True thymic hyperplasia without any other disease is extremely rare and only seven well documented examples could be found in a review of the literature. Enlargement of the thymus gland is reported as a form of rebound phenomenon in a number of conditions like recovery from severe stress situations, after administration of steroids, and after treatment of malignant tumors. Finally, thymic hyperplasia has been described in association with endocrine abnormalities, sarcoidosis, and Beckwith-Wiedeman syndrome.