Rheumatoid factors (RFs) are auto-antibodies, mostly of the IgM isotype, that specifically bind to the Fc portion of IgG. RFs are transiently produced in healthy individuals in response to infections and after immunization with mismatched red blood cells (RBCs). RFs are chronically produced in patients suffering from rheumatoid arthritis, Sjö gren's syndrome and in hepatitis C virus (HCV)-induced type-II mixed cryoglobulinemia (MC-II) (reviewed in Newkirk 1 ). Analyses of RFs in MC-II and in donors immunized with mismatched RBCs revealed four groups of stereotyped immunoglobulin (Ig) V H -D H -J H rearrangements, each with distinct heavy-chain complementary-determining region 3 (HCDR3) amino acid sequences: two with IGHV1-69/JH4 rearrangements, designated V1-69-RF and RF-WOL, and two with IGHV3-7/JH3 and IGHV4-59/JH2 rearrangements, designated V3-7-RF and V4-59-RF, respectively. [2][3][4] Remarkably, similar stereotyped RF-rearrangements are frequently expressed in malignant B-cell lymphomas. 2,5,6 Previously, we have shown that recombinantly produced V1-69-RF, V3-7-RF and RF-WOL, derived from gastric and salivary gland marginal zone B-cell lymphomas (MZBCL), bind with high-affinity to IgG in vitro. 2,7 V1-69-RF, V3-7-RF, RF-WOL and V4-59-RF rearrangements are also frequently expressed in HCV-associated lymphomas, splenic marginal zone lymphomas and in individual cases of ocular MZBCLs and diffuse-large B-cell lymphomas. 5,6,[8][9][10] Recently, Kostareli et al. 10 reported 12 cases of B-cell chronic lymphocytic leukemia (CLL) expressing V4-59-RF and Fazi et al. 11 reported two cases of V3-7-RF in monoclonal B-cell lymphocytosis.In this study, we analyzed HCDR3 amino acid sequences of 81 IGHV3-7-expressing CLL and identified 3 cases with strong homology to 25 previously reported V3-7-RFs from both healthy and malignant B-cells (Table 1, Supplementary Table 1). These 25 V3-7-RF cases include 9 with proven RF-activity in vitro. The three newly found CLL cases, CLL81, CLL311 and CLL416, utilized the IGHD3-22 gene segment and the IGHJ3 segment shared by 15/24 and 22/24 of V3-7-RFs, respectively. The CLL V3-7-RFs displayed 470% of homology with a V3-7-RF HCDR3 consensus sequence, defined by the amino acids used by the majority of V3-7-RF cases (Table 1). Of note, the V3-7-RFs also shared amino acids encoded by non-templated N-region nucleotides (Figure 1a). Two of the newly identified CLL V3-7-RF cases (CLL81 and CLL416) expressed the stereotyped IGKV3-15 Ig light chain (IgV L ) reported in 10/10 V3-7-RF cases (Table 1). In CLL311, the V3-7-RF Ig heavy chain (IgV H ) was paired with an IGKV3-20-encoded IgV L . Remarkably, similar IGKV3-20 rearrangements were found in the other groups of stereotyped RFs.The CLL V3-7-RFs were heavily mutated (94.5±1.9% average homology to the IGHV3-7 germline) and shared replacement mutations Q58P, Y66F and Q90E (Figure 1a and Supplementary Table S2). Identical somatic mutations are also frequent among