OBJECTIVE: To evaluate whether the single nucleotide polymorphism (SNP), Asp1104His (G3507C), in the XPG gene affects malignant phenotypes of nonmuscle-invasive urinary bladder neoplasms (NIBN), by investigating associations between the SNP and clinicopathological variables in patients with NIBN. PATIENTS AND METHODS: The 233 patients constituted newly diagnosed cases of primary NIBN in the Stockholm area. The Asp1104His polymorphism in the XPG gene was genotyped using a polymerase chain reaction-restriction fragment length polymorphism technique. RESULTS: The GC + CC genotypes were more frequent in stage pT1 tumours at initial diagnosis than pTa (odds ratio 1.9, 95% confidence interval 1.0-3.5, P = 0.048). The difference was larger in the young group (4.6, 1.9-11.8, P = 0.001). In the young group, the GC + CC genotypes were significantly more frequent in high-grade than in low-grade tumours (3.1, 1.5-6.8, P = 0.004) whereas in the older group the genotypes were less frequent in high-grade tumours (0.3, 0.1-0.7, P = 0.007). The XPG genotypes were not associated with tumour recurrence, stage progression or survival. CONCLUSION: These results suggest that the SNP in the XPG gene might be related to tumour invasiveness in NIBN.