Treatments for non-Hodgkin's lymphomas vary widely. Because all treatments are not useful to all patients, the non-Hodgkin's lymphomas must be divided into clinically relevant subgroups. Previous systems used to subdivide the non-Hodgkin's lymphomas were based on morphology. Later systems added immunologic subgrouping. The International Lymphoma Study Group recently has proposed that lymphomas be grouped as clinical-pathologic entities. Diagnoses based on this system were much more accurate than those using previous systems, but much work remains to be done in the classification of these cancers.