Bone marrow and lymphoid tissue can be damaged by medications or radiation and are particularly susceptible to injury in bone marrow transplant recipients. Iatrogenic bone marrow suppression is a common in-hospital complication, the therapeutic management of which is difficult. In patients with cancer, aggressive treatment usually induces bone marrow damage, but this can be prevented using specific colony-stimulating factors. Heparin-induced thrombocytopenia is a distinct lesion with unusual clinical features. Its two types of manifestation are presented in this chapter, together with other lymphoid tissue-specific iatrogenic disorders.