The recent Revised European-American Classification of Lymphoma (REAL) classification system has been shown to allow easy, accurate, and reproducible identification of several clinically distinctive lymphoma subtypes. Many of these well-recognized lymphoma entities are relatively rare, as shown by a recent large survey of more than 1400 non-Hodgkin's lymphoma (NHL) cases from eight different countries. The purpose of this article is to summarize the present information known about these less common entities. Particular attention will be paid to the management problems of the following subtypes: the marginal-zone B-cell lymphomas of nodal type (or monocytoid lymphoma, comprising 1.8% of total cases in the above-mentioned series), the extranodal marginal-zone B-cell lymphomas (or mucosa-associated lymphoma tissue [MALT] lymphomas, representing 7.6% of the cases), the splenic marginal-zone B-cell lymphomas (< 1% of cases), the mantle cell lymphomas (6% of cases), and the primary mediastinal large B-cell lymphomas (2.4% of cases). Also, the main non-cutaneous peripheral T-cell lymphoma types, which including the natural killer (NK) disorders comprise less than 12% of all lymphoma cases, are discussed.