Mutations of the methylenetetrahydrofolate reductase (MTHFR) gene have been shown to be associated with a predisposition to developing diabetic nephropathy (DN) in specific populations. The frequency of two MTHFR mutations, a recently described mutation in the human MTHFR gene A1298C and C677T, whose association with DN is already known, was determined in an Israeli Jewish population with type 2 diabetes mellitus (DM). Both A1298C and C677T are highly prevalent in the diabetic population with allele frequencies of 0.35 and 0.36, respectively. The genotype frequency and allele frequency for these two polymorphisms in patients who are normoalbuminuric (n = 55) were compared with those of patients who had either micro- or macroalbuminuria (n = 43). For both polymorphisms, there were no significant differences in either the genotype distribution or allele frequency in patients with or without DN. However, in patients with serum folate <15.4 nmol/L, there was a greater incidence of DN in those patients who were homozygous or heterozygous for the C677T mutation. For the A1298C mutation, there is evidence suggesting that the homozygous state may be protective in patients with low-normal serum folate. Folate supplementation in diabetic patients with the C677T mutation and low-normal serum folate may prevent the onset or retard the progression of DN.