The gene encoding endothelial nitric oxide synthase (eNOS) is involved in abnormalities in nitric oxide (NO) synthesis that mediates functional damage of vascular cells, especially of endothelial cells (ECs), a common characteristic in cardiovascular diseases. In Fabry's disease, the characteristic mutation in the alpha-galactosidase A (alpha-gal A) gene induces large deposits of glycosphingolipids, particularly concentrated in ECs, a process associated with endothelial dysfunction. To determine whether in addition to alpha-gal A gene mutations, eNOS genetic variations are implicated in this process, we examined the genotypes of the missense Glu298Asp (G894T) variant in exon 7 and 27-bp tandem repeats in intron 4 (4b/a) in 19 patients with Fabry's disease, and 39 normal volunteers. The results showed that both varials have a significant association with Fabry's disease. The frequencies of mutant Glu/Asp + Asp/Asp genotypes and Asp allele are significantly higher in Fabry's disease (68.4%, p = 0.044, and 47.4%, p = 0.022, respectively) than in controls (46.7% and 25%, respectively). The frequencies of eNOS 4b/a polymorphisms are also significantly different in Fabry's disease when compared to controls. The mutant 4b/a + 4a/a genotype frequencies are 55.5% (p = 0.032) and 4a allele 27.8% (p = 0.05) compared with controls (23.1% and 12.8%, respectively). These results indicate that more than half of the patients with Fabry's disease carry the Glu298Asp variant ( approximately 68%) and/or the 4b/a polymorphism ( approximately 55%). To the best of our knowledge, this is the first report showing an influence of eNOS gene polymorphisms in patients with Fabry's disease.