Non-Hodgkin's lymphomas (NHLs) are a heterogeneous group of lympho-proliferative disorders, mainly originating in lymphoid tissues and other extranodal organs, with different patterns of behavior. Prognosis depends on the histo-pathologic type, prognostic factors, and treatment. According to the WHO classification (2001), the NHLs are divided into two prognostic groups: the indolent lymphomas (follicular lymphoma, marginal zone B-cell lymphoma, etc.) and the aggressive lymphomas (diffuse large B-cell lymphoma, peripheral T-cell lymphoma, etc.). Indolent NHLs have a good prognosis, with median survival as long as 10 years, and early stage (I and II) indolent NHLs can be treated with radiation therapy alone, with 70% to 90% 5-year overall survival rates. The aggressive NHLs have shorter natural histories, but the number of patients cured with intensive chemotherapy currently is increasing. In general, overall survival at 5 years is approximately 50% to 60%. Patients with stage I and contiguous stage II aggressive NHLs enjoy excellent survival rates when treated with a combined modality including chemotherapy (CHOP) and radiation therapy. The radiation dose for NHLs varies from 25 to 50 Gy and is dependent on pathologic type and the organs at risk. Radiation fields are basically limited to involved regions or extended to immediately adjacent sites. Localized presentations of extranodal NHLs can be treated with involved-field techniques with significant success. However, the long-term adverse reactions must be considered carefully.