Lymphadenopathies may occur in patients treated with a variety of immunomodulatory drugs. Drugs such as prednisone, azathioprine, methotrexate, cyclosporine, and others are used to diminish the symptoms of hyperimmune reactions in recipients of organ transplants and in patients with autoimmune diseases. However, treatments intended to modulate immune reactions, particularly when extended for long periods of time, have the inadvertent effect of predisposing patients to a variety of lymphoproliferative disorders. These range from benign reactive lymphadenopathies to atypical lymphoproliferative lesions to Hodgkin and non-Hodgkin lymphomas. A particular feature of such lymphoproliferations is that they may regress on cessation of treatment. In some cases, even lymphomas with demonstrated monoclonality have regressed after the discontinuation of immunomodulatory drugs.