Lymphoproliferative pulmonary neoplasms can occur as primary pulmonary lymphomas or because of secondary pulmonary involvement. Neoplastic disorders may be difficult to differentiate from reactive pulmonary lymphoproliferative disorders, and immunohistochemical evaluation is often required to differentiate the 2 types of lesions.Neoplastic lymphoproliferative disorders are monoclonal lesions. Most affected patients present with systemic complaints, and imaging findings typically include nodules, masses, and lymphadenopathy.Primary pulmonary lymphomas are rare and account for less than 4% of the lymphomas that arise in extranodal sites. Secondary pulmonary lymphomas can affect the lung via hematogenous dissemination or by secondary involvement from tumor in adjacent or contiguous sites. Neoplastic lymphoproliferative lesions also include leukemia and plasma cell neoplasms. Posttransplantation lymphoproliferative disorders constitute a special type of lymphoid proliferation occurring in the setting of the chronic immunosuppression required for solid organ and bone marrow transplantation.