In B-cell chronic lymphocytic leukemia (B-CLL), somatic mutation of IgVH genes defines a subgroup with favorable prognosis, whereas the absence of IgVH mutations is correlated with a worse outcome. Mutations of the BCL-6 gene are also observed in a subset of B-CLL, but the clinical significance of this molecular alteration remains uncertain. We examined the distribution of IgVH and BCL-6 gene mutations in 95 well-characterized patients with Binet stage A B-CLL, and correlated them with clinical, laboratory, cytogenetic findings and disease progression. Mutations of the BCL-6 gene were observed only in cases harboring mutated IgVH. Unexpectedly, coexistence of IgVH and BCL-6 mutations was correlated with shorter treatment-free interval (TFI) compared to cases harboring only IgVH mutation (median, 55 months vs not reached; P=0.01), resembling the clinical course of unmutated IgVH cases (median TFI, 44 months). As expected, deletions of 17p13 (P53 locus) and 11q22 (ATM locus) were observed in cases with unmutated IgVH, except one patient who showed mutations of both IgVH and BCL-6. No other statistically significant differences were observed among the genetic subgroups. Our data indicate that BCL-6 mutations identify a subgroup of Binet stage A B-CLL patients with a high risk of progression despite the presence of mutated IgVH gene.