The thymic epitheliums educate the pre-T lymphocytes from bone marrow by either direct contact or humoral stimulation and support their differentiation, proliferation and maturation. Thymic abnormalities include pathological involution, germinal center formation and tumor. Historically, many disorders associated with thymic abnormality have been reported. In this lecture, the structures and functions of human thymus, and immunological and hematological disorders related to thymic abnormalities such as myasthenia gravis, pure red cell aplasia, immunodeficiecy syndromes, immunoglobulin dyscrasias, acute T cell-leukemia, Hodgkin disease and lymphocytic lymphoma were reviewed. These extensive reviews suggested “Pharyngeal Pouch Syndrome” and it's significant roles in hematology.