During the last ten years the combined efforts of pathologists and molecular biologists have helped define several new lymphoma diagnostic categories. In particular, the recognition of chromosomal translocations which have activated the BCL1 and BCL2 proto-oncogenes have strong associations with specific types of non-Hodgkin's malignant lymphomas such as mantle cell lymphoma and follicular center cell lymphoma, respectively. This review will attempt to summarize our current understanding regarding the contributions of BCL1 and BCL2 to lymphomagenesis and diagnosis.