The metastasis-suppressing role of the nm23 gene in the metastatic spread of malignant tumor is still debated. We examined the nm23-H1 protein expression and gene mutation in non-Hodgkin's lymphomas to compare with the clinicopathologic parameters. The expression of nm23-H1 protein was immunohistochemically examined in 150 cases of non-Hodgkin's lymphomas; 85 diffuse large B cell lymphomas (DL-BCL), 18 marginal zone B cell lymphomas (MZL), 3 mantle cell lymphomas, 25 peripheral T cell lymphomas, not otherwise specified (TCLNOS), and 19 NK/T cell lymphomas (NK/T). Eighty-one cases (58 DLBCL, 6 MZL, 4 TCLNOS, and 13 NK/T) were studied for nm23-H1 gene mutation in exon 1 to 5. The high expression of nm23-H1 protein was associated with the high IPI score (p=0.019) and the low survival rate of the patients (p=0.0039). The gene mutation of nm23-H1 was detected in 10.3% of DLBCL and 30.7% of NK/T; but none in MZL and TCLNOS. The mutation was found in exon 1 in 5 cases, exon 2 in two cases, exon 4 in one case and both exon 1 and 2 in two cases. Our results suggest that the expression of nm23-H1 protein can be used as a poor prognostic marker in non-Hodgkin's lymphomas, and the mutational change of gene may operate in the lymphomagenesis.