One of the features of bladder cancer is progressive genomic instability. It has been suggested that the lost or gained regions harbor tumor suppressor genes and oncogenes, respectively. The recent introduction of high-resolution single nucleotide polymorphism (SNP) arrays for scoring of allelic imbalance can be used to pinpoint very narrow regions of allelic imbalance (potential chromosomal loss). Allelic imbalance (AI) is defined as the conversion of a heterozygous SNP in germ line (blood) to a homozygous SNP in tumor tissue. Koed et al. have looked at AI related to disease course and at clonality by analyzing the recovery of AI from tumor to tumor in the same individual. They found AI to be strongly related to stage and TP53 mutation, and were able to define two separate groups of stable (blue dots) and unstable (red dots) tumors. The unstable tumors had a very high frequency of common allelic imbalances in three chromosomal areas. In total, 91 % of the unstable tumors had AI in two areas on chromosome 8p, while all (100%) of the unstable tumors had AI in an area on chromosome 17p close to the TP53 locus. These findings show the power of high-resolution SNP arrays for defining clinically relevant AI, that may be used for predictive purposes and for identifying new tumor suppressors. For details, see article by Koed et al. on page 34 of this issue.