When stratified by the source of controls, our results found little evidence of an association between XRCC1 Arg399Gln polymorphism and increased risk of glioma among Caucasians using population-based controls but not using hospital-based controls, indicating the importance of the use of proper and representative cancer-free control subjects because the allele distribution in hospital-based controls may not be very representative of the general population. The gene discussed is XRCC1; the disease is central nervous system cancer.