High dose total body irradiation is widely used in conditioning regimens to treat patients undergoing bone marrow transplantation. Radiation-related complications observed in 67 patients who received total body irradiation and their correlation with physiopathological mechanism of clinical manifestations are discussed. Interstitial pneumonitis occurred in 9 patients in our study (14%); the relationship between the incidence of interstitial pneumonitis and many factors such as irradiation treatment techniques, pre-graft chemotherapy, bone marrow malignant as well hereditary diseases, are discussed and related to a detailed literature review. Radiation techniques are different in leukemic and thalassemic patients.