The tendency to evolve into acute leukemia is a well-known characteristic of polycythemia vera (PV), which is shared with the remaining chronic myeloproliferative disorders and increases after the administration of cytotoxic agents. Acute transformation is usually of myeloid phenotype, whereas acute lymphoid leukemia (ALL) following PV is seldom observed. A 63-year-old woman is described who developed ALL at 6 years from the initial diagnosis of PV, for which she had received radioactive phosphorus and hydroxyurea. The ALL was of B-cell type, corresponding to the L-3 subtype of the FAB classification. Despite the administration of combination chemotherapy the patient died shortly after the diagnosis of acute leukemia. The present case adds to seven previously described patients with the above association, all of whom had received cytotoxic therapy for PV. Median interval from PV to ALL diagnosis was 10 years, and there was a predominance of the B-cell phenotype. The prognosis was poor since all but one of the patients had a short survival after ALL diagnosis. The possible etiological and pathogenetic link between PV and the subsequent ALL is discussed.