Non-Hodgkin's lymphomas are a heterogeneous group of malignancies of the lymphoid system. The exact etiology for most lymphomas has not been determined, but both viral and bacterial infections have been shown to be important etiologic factors. The WHO classification of hematopoietic and lymphoid tumours classifies lymphomas into B-cell and T-cell neoplasms. B-cell lymphomas account for more than 85% of all lymphomas. The Ann Arbor staging classification has been adopted by the AJCC and UICC as a standard for classifying extent of anatomic disease. The two most common histologic disease entities are follicular lymphomas and diffuse large B-cell lymphomas. The management of follicular lymphomas is used as a paradigm for the management of all indolent lymphomas. Radiation therapy is used for stage I and II disease, while alkylating agent chemotherapy, immunotherapy and radioimmunotherapy are most frequently used in stage III and IV disease that requires treatment. Most patients with follicular lymphoma enjoy prolonged survival, but at present there is no evidence that those with stage III and IV follicular lymphoma can be cured. Diffuse large B-cell lymphomas serve as a paradigm for treating aggressive lymphomas. Stage I and II diffuse large cell lymphomas are generally treated with combined modality therapy with doxorubicin-based chemotherapy followed by involved field radiation therapy, while those with stage III and IV disease are treated with chemotherapy alone. Patients who fail initial management are treated with further chemotherapy. High-dose chemotherapy with stem cell rescue has been shown to be particularly effective as salvage treatment for diffuse large cell lymphomas. The management of a heterogeneous group of primary extranodal lymphomas in general follows the above treatment principles, with additional treatment being required for those with a high risk of CNS failures, or involvement of contralateral paired organs. The management of MALT lymphomas, especially gastric MALT lymphoma, deserves special attention because of the high response rate to Helicobacter pylori eradication therapy.