Follicular lymphoma is characterized by chromosomal translocation involving BCL2 and immunoglobulin heavy chain genes (IgH). That the incidence of follicular lymphoma and the previously reported frequency of BCL2 translocation are lower in Asians than in Caucasians implies a different molecular pathology. The study of BCL2 rearrangement will yield deeper insights into the pathogenesis of follicular lymphomas and into clinical applications of molecular diagnosis for Asian follicular lymphoma patients. BCL2 /IgH translocation was analyzed in paraffin-embedded tissues from follicular lymphoma patients by using polymerase chain reaction (PCR) analysis of the major breakpoint region (MBR), the intermediate cluster region (ICR), and the minor cluster region. In addition, fluorescence in situ hybridization (FISH) analysis with split-signal BCL2 probes was performed. PCR analysis revealed BCL2 rearrangement in 12 (23.5%) of 51 cases (10 MBR and 2 ICR breakpoints). This frequency is lower than the frequencies reported from Western countries (40%-60%). DNA sequencing of the breakpoints revealed nucleotide insertions suggesting V(D)J recombination-mediated mechanisms. On the other hand, FISH analysis revealed 11 (84.6%) of 13 cases with positive signals for BCL2 translocation. Our results suggest that BCL2 translocation is essential for the pathogenesis of follicular lymphoma in Thai patients. In addition, the data demonstrate the low sensitivity of the PCR for diagnostic testing and suggest that split-signal FISH is the method of choice.