Three genome-wide association studies in Europe and the USA have reported 8 urinary bladder cancer (UBC) susceptibility loci. Using extended case and control series and 1000 Genomes imputations of 5,340,737 single nucleotide polymorphisms (SNPs), we searched for additional loci in the European genome-wide association study (GWAS). The discovery sample set consisted of 1,631 cases and 3,822 controls from The Netherlands and 603 cases and 37,781 controls from Iceland. For follow up, we used 3,790 cases and 7,507 controls from 13 sample sets of European and Iranian ancestry. Based on the discovery analysis, we followed up signals in the urea transporter gene SLC14A. The strongest signal at this locus was represented by a SNP in intron 3, rs17674580, that reached genome-wide significance in the overall analysis of the discovery and follow-up groups: OR = 1.17, P = 7.6×10­11. SLC14A1 codes for urea transporters that define the Kidd blood group and are crucial for the maintenance of a constant urea concentration gradient in the renal medulla and, through this, the kidney's ability to concentrate urine. It is speculated that rs17674580, or other sequence variants in LD with it, indirectly modify UBC risk by affecting urine production. If confirmed, this would support the 'urogenous contact hypothesis' that urine production and voiding frequency modify the risk of UBC.