Carbamoyl phosphate synthetase 1 (CPS1) is a key gene in the first step of urea cycle and has been correlated with nitric oxide level and vascular smooth muscle activity. A functional single-nucleotide polymorphism C/A at position 4217 in CPS1 (National Center for Biotechnology Information SNP database no. rs7422339, T1405N) was reported to be associated with high homocysteine (Hcy) plasma values. Although genetic variants of methylenetetrahydrofolate reductase (MTHFR) gene are known to influence Hcy concentration, other genetic determinants of Hcy remain largely unknown. The association between the CPS1 rs7422339 and the risk of hyperhomocysteinemia in Latin American populations is unknown. Here, we study this association in 100 patients having hyperhomocysteinemia without MTHFR c.677C>T polymorphism and 100 controls. CPS1 rs7422339 was studied using polymerase chain reaction and enzymatic restriction. Comparisons of the CPS1 rs7422339 genotype distributions revealed a significant difference between groups (P = 2.3 × 10−3). Patients carrying polymorphic allele showed almost 3 times higher risk (odds ratio [OR] = 2.47) of hyperhomocysteinemia than wild-type allele, suggesting that rs7422339 SNP is associated with high Hcy levels in the Argentine population.