Background/Aims: Polymorphism of the endothelial nitric oxide synthase (ecNOS) gene may be involved in renal disease. Recently, T<sup>-786</sup>→C polymorphism affecting ecNOS gene transcription has been reported. To clarify the role of T<sup>-786</sup>→C polymorphism in renal disease, we investigated hemodialysis patients and healthy controls for this polymorphism and we compared its frequency with that of intron 4 polymorphism in the hemodialysis patients. Methods: The subjects were 252 patients who had been on hemodialysis for less than 2 years (168 with nondiabetic nephropathy and 84 with diabetic nephropathy) and 187 healthy controls. T<sup>-786</sup>→C polymorphism was detected using polymerase chain reaction-restriction fragment length polymorphism analysis. Results: The frequencies of the T/ C and C/ C genotypes were significantly higher in the nondiabetic hemodialysis patients than in the controls (odds ratio 1.41; 95% Cl 1.03–2.00), and were also significantly higher in the diabetic hemodialysis patients than in the controls (odds ratio 1.56; 95% Cl 1.02–2.41). In addition, T<sup>-786</sup>→C polymorphism and intron 4 polymorphism showed strong linkage disequilibrium. Conclusion: T<sup>-786</sup>→C polymorphism may be involved in the progression of both nondiabetic and diabetic nephropathy, along with intron 4 polymorphism.