Two genetic loci, PKD1 and PKD2, have been identified as being responsible for ADPKD, but the presence of an intrafamilial clinical diversity suggests that there are disease-modifying loci. We studied the associations between polymorphism in the ecNOS gene, which are known to be associated with chronic tubulointerstitial and vascular changes, and ADPKD progression in Korean patients. A total of 112 individuals who had ADPKD and 41 normal control subjects were genotyped by PCR-RFLP, the Glu298Asp variant of ecNOS gene was discriminated with MboI. The distribution of the alleles for the ecNOS Glu298Asp polymorphism in ADPKD was: G 88%, T 12%, which was similar to the result of Korean population (95:5, p = 0.128) but different from Western controls (65:35, p = 0.000). No differences were found between the CRF and the non-CRF groups (p = 1.000) or the early hypertension and the normotension groups (p = 1.000). In conclusion, our results suggest that the polymorphism at Glu298Asp of ecNOS has no association with the renal progression in Korean ADPKD patients.