We report a series of 37 cases of lymphoproliferative disorders with 3q27 structural chromosomal abnormalities. Breakpoints at 3q27, the site of the bcl-6 gene, appear in a broad range of B cell lymphoma histologies but are most frequently detected in follicular lymphomas lacking a t(14;18) and diffuse large cell lymphomas. The majority of 3q27 rearrangements result from translocations involving the immunoglobulin heavy or light chain genes, however, involvement of other partner chromosomes is also observed. Molecular rearrangement of bcl-6 is demonstrable in a subset of cases. Bcl-6 is a recently identified gene encoding a zinc-finger protein. It is normally expressed in germinal center B cells where it is believed to have a developmental or differentiation function. Transcriptional deregulation of bcl-6 through translocations, submicroscopic molecular rearrangements or point mutations may be responsible for this gene's putative lymphomagenic potential.