AbstractIn this study we determined the effect of single nucleotide polymorphisms in the XPG gene on DNA repair and breast cancer susceptibility. Ninety individuals, with previously studied DNA repair rate at 24 hr of 2 types of UV‐specific cyclobutane pyrimidines dimers (CPDs) in skin were genotyped for XPG polymorphism at codon 1104 (exon 15 G>C; Asp > His). The repair rate of TT=C dimer was similar in both wild‐type GG homozygotes and GC heterozygotes, whereas, for TT=T, dimer repair was non‐significantly (Student's t‐test, p = 0.34) lower in GC heterozygotes than wild‐type GG homozygotes. Genotyping of 220 breast cancer cases and 308 controls for the same single nucleotide polymorphism in exon 15 of the XPG gene exhibited marginally significant increased frequency of the variant allele (χ2 3.84, p = 0.05; OR 1.33, 95% CI 1.0–1.8) in cases (C‐allele 0.29) compared to controls (C‐allele 0.24). Combined heterozygote and variant homozygote genotype frequency was also higher in cases than controls (χ2 4.79, p = 0.03; OR 1.50, 95%CI 1.04–2.16). © 2002 Wiley‐Liss, Inc.