A t(14;18) translocation is closely associated with the follicular lymphoma but is also seen in diffuse B cell lymphomas with a previous history of a follicular lymphoma as well as de novo diffuse lymphomas. Estimation of the frequency of t(14;18) in follicular lymphoma vary widely from 33 to 89%. Furthermore, no extensive data have been published on the frequency of t(14;18) in Turkish cases of follicular lymphoma. Representative tissue blocks from 67 patients with follicular lymphoma, 12 cases of diffuse large B cell lymphomas and 11 cases of reactive hyperplasias were examined for the presence of this translocation using PCR. DNA probes capable of detecting rearrangement at both the major and minor break point regions were employed. We could detect t(14; 18) in 46 out of 67 cases (68.7%) of follicular and 25% of diffuse large B cell lymphomas. In follicular lymphomas 64.2% of these break points were at mbr and 4.5% were at the mcr region. Review of the literature showed that comparable results have been obtained previously using molecular techniques. Our data showed that despite the relative infrequency of follicular lymphomas in the Turkish population these lymphomas share a common molecular pathogenesis with involvement of bcl-2 gene and background incidence of such rearrangement is similar in all populations, regardless the incidence of folicular lymphoma. (C) 2000 Elsevier Science Ltd. All rights reserved.