The t(14;18) translocation, which involves the bcl-2 oncogene, occurs in follicular lymphomas (FL) at two common sites: the major breakpoint region (MBR) and the minor cluster region (mcr). The biological and clinical significance of these breakpoints is unknown. The bcl-2 breakpoint site was determined in 247 previously untreated patients (49% men; median age 52 years) with indolent FL (155 grade I, 83 grade II, and 8 grade III) to correlate it with pretreatment characteristics, response, and outcome. The bcl-2 breakpoint site was determined by a polymerase chain reaction method of peripheral blood (all cases), bone marrows (149 cases), and fresh lymph node biopsy specimens (68 cases). The breakpoint site occurred at MBR in 175 cases (71%) and at mcr in 27 (11%). In 45 cases (18%), no breakpoint was detected (germline). No significant relationship was found between the rearrangements and the expression of BLC-2 and BAX proteins. Patients' germline for MBR and mcr tended to present more frequently with stage IV disease and higher beta2-microglobulin (beta2M) levels, whereas mcr-rearranged patients presented more frequently with early stage and normal beta2M. The complete response rate of germline patients was significantly lower than that of MBR and mcr patients. An estimated 3-year failure-free survival (FFS) for mcr, MBR, and germline cases was 95%, 76%, and 57%, respectively (P <.001). The bcl-2 breakpoint site was independent of serum beta2M and lactate dehydrogenase in its correlation with FFS. In conclusion, the bcl-2 rearrangement site is an important prognostic factor in indolent FL, useful to identify patients who may require different treatment.