Increasing knowledge about the biology of the non-Hodgkin's lymphomas has led to new approaches in classification. Rather than grouping lymphomas simply based on cell size, cell shape, and growth pattern, it is now possible to identify distinctive clinicopathologic entities. In many cases, the existence of specific immunologic and/or genetic features has confirmed the existence of these distinctive types of lymphoma. Since patients will be given these diagnoses by pathologists, it is important that clinicians be knowledgeable with regard to their clinical characteristics. The findings for the 13 most common lymphoma types that will be encountered in clinical practice are presented here.