Background and Aims: Increased synthesis of several urinary proteins including osteopontin (OPN) has been shown to be associated with stone formation within the urinary tract. The objective of this study was to analyze the genotype distributions and allele frequencies for OPN gene promoter T-593A and C6982T (in exon 7) polymorphisms among patients with kidney stones. Methods: In this case-control study, the study group consisted of 121 patients with radiologically confirmed nephrolithiasis. Genomic DNA from patients and control cases (n = 100) was analyzed by single-strand conformation polymorphism method and nucleotide sequence analysis. Results: Homozygous carriers of the T-593T genotype were more frequent, but carriers of the A-593A genotype were less frequent in patients than in controls. There was also an increase in -593T allele (88% in patients vs. 79% in controls) and decrease in -593A allele frequencies (21% in control vs. 12% in patients) in the nephrolithiasis groups (p = 0.013). The carriers of C6982C genotype were less frequent, but marked increases in T6982T genotype (25.6% in patients vs. 7% in controls, p = 0.001) and 6982T allele frequency (53.3% in patients vs. 37.5% in controls, p = 0.001) were noted in patients of Turkish ancestry. Conclusions: These results are the first to demonstrate the existence of T-593A promoter polymorphism of the OPN gene and significant association with risk of developing nephrolithiasis. Our results showed marked associations between polymorphisms (C6982T and T-593A) of the OPN gene and the stone-forming phenotypes in the Turkish population. © 2010 IMSS.