Given the importance of mismatch repairing genes in keeping the genetic stability in cells, any alterations in their structure or function could generate instability in the genome and predispose the development of oncogenic processes. hMSH2 is the principal gene involved in the post-replicating DNA mismatch repair system. In this study, exon 13 of the hMSH2 gene was analyzed in different neoplasias, leukemias and lymphomas. The aim of our work was to determine the association between the presence of polymorphisms in this region with the development of alterations in the hematological system. The 227 samples including lymphoma, leukemia and myelodysplasic syndromes, where analyzed by PCR-SSCP followed by automated sequencing. A single nucleotide polymorphism was found in 30 individuals. This polymorphism is a T to C substitution at the -6 intronic splice acceptor site of exon 13 of hMSH2 gene [gIVS12-6T > C]. In the lymphoma group the polymorphism frequency found was 0.09, with statistical significant differences (p < 0.01) when compared to the control group. On the other hand, the frequency of the leukemia group was the same of that of the control group (0.05). These findings agree with previous research results of other investigation groups. The results suggest a probable association of the polymorphism with the development of lymphomas but not with leukemia.