Background: After angioplasty, veins are more prone to intimal hyperplasia than arteries. Veins tend to produce less nitric oxide (NO), which could lead to endothelial dysfunction. Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of NO synthase and contributes to cardiovascular disease. In humans, dimethylarginine dimethylaminohydrolase 1 (DDAH1) is the major enzyme for ADMA degradation. In this study, we aim to determine whether venous intimal hyperplasia in hemodialysis (HD) vascular access is influenced by common polymorphisms in the DDAH1 genes. Methods: This is a prospective observational cohort study. A total of 473 HD patients referred for the angioplasty of vascular access were enrolled. There were 190 arteriovenous grafts (AVG) and 283 arteriovenous fistulas (AVF). The follow-up lasted for 2 years after the interventions. Seven single nucleotide polymorphisms (SNPs) in DDAH1 were genotyped and ADMA were measured at baseline. The primary outcome was restenosis after angioplasty. Results: Among the 7 SNPs, plasma ADMA levels were significantly different in DDAH1 rs233112 (GA + GG vs. AA, 0.86 ± 0.23 vs. 0.82 ± 0.19 μM, p = 0.03) and rs1498373 (CT + TT vs. CC, 0.87 ± 0.23 vs. 0.82 ± 0.20 μM, p = 0.02) genotypes. The AVF group with GG + GA genotype of rs233112 and CT + TT genotype of rs1498373 had higher risks of early restenosis at 3 months. In the AVG group, only GG + GA genotype of rs233112 was associated with early restenosis. A combined analysis of AVG and AVF groups showed that patients with rs233112 GA + GG genotype and rs1498373 CT + TT genotype had higher risks of early restenosis (both p < 0.001). The multivariate analysis results showed that the association of these genotypes with early restenosis is independent of clinical, access, or biochemical factors. Conclusions: Our findings suggest that certain DDAH1 polymorphisms modulate circulating ADMA levels and are associated with venous intimal hyperplasia.