We report the progression of splenic marginal zone lymphoma (SMZL) with circulating villous lymphocytes to Burkitt lymphoma with the presence of a t(8;14)(q24;q32) followed by a highly aggressive course. While the initial indolent lymphoma had an IgM lambda immunophenotype the Burkitt lymphoma was IgM kappa-positive. Immunoglobulin heavy chain gene (IGH) sequence analysis showed no identity between the two clones. We conclude that Burkitt lymphoma can occur in patients with SMZL, although not necessarily of identical clonal origin.