Chromosomal aneuploidy is associated with invasive bladder cancer and one of the genes implicated in these changes is Aurora-A/STK15/BTAK, that is localized on chromosome 20q13 and encodes a centrosome-associated serine/threonine kinase. To better understand the association between Aurora-A/STK15 expression, tumor aneuploidy and clinical prognosis, we sought to determine whether overexpression of Aurora-A/STK15 in cultured urothelial cells facilitated chromosomal instability. Using immunofluorescence staining, Northern and Western blot analyses, we verified that overexpression of Aurora-A/STK15 in bladder tumor cell lines enhanced chromosomal instability. Additionally, we observed that some bladder tumor cell lines expressed more Aurora-A/STK15 than cultured normal urothelial cells and that Aurora-A/STK15 expression was higher in an immortalized E7 urothelial cell line having 20q amplification than in an E6 line lacking 20q amplification. These results were consistent with our observations of higher mRNA levels in some T3 invasive bladder tumors than in T1 superficial tumors and adjacent normal bladder tissue. Overall our results suggest that overexpression of Aurora-A/STK15 in bladder tumor cells contributes to tumor progression by promoting chromosomal instability leading to aneuploidy.