The non-Hodgkin's lymphomas are a diverse group of diseases characterized by enlargement of the lymph nodes and are indolent or aggressive. The histopathologic subtype provides the best guide to the nature of these diseases. In most patients the etiology is unknown. Painless peripheral adenopathy is the usual presenting feature. A careful clinical staging without laparotomy is recommended to establish disease extent, prognosis and treatment. In patients with indolent (low grade) lymphomas, a period of observation prior to treatment may be appropriate if the patient is asymptomatic. Symptomatic patients with low grade lymphoma require therapy. For patients with aggressive disease (intermediate or high grade), immediate treatment with curative intent is indicated. High dose therapy with bone marrow transplantation may be used to cure a small number of patients who relapse following initial chemotherapy.