We have previously observed loss of heterozygosity (LOH) at a single locus (del‐27) on human chromosome 5p13‐12 to correlate with bladder tumor progression. In this study, we examined 33 bladder tumors for their pattern of allelic loss on chromosome 5p using 7 microsatellite markers. In 14 of 15 bladder tumors with LOH at locus del‐27, allelic loss was confined to chromosomal region 5p13‐12. This region included the microsatellite marker D5S2025 that showed LOH in 5 of 11 (45%) informative cases with LOH at del‐27. This suggests that D5S2025 and del‐27 are located within a single critical region of LOH on 5p13‐12 harboring a tumor suppressor gene involved in bladder tumor progression. Recurrent LOH at other loci was observed at microsatellite markers located at 5p15. However, these losses appeared to be independent of LOH at 5p13‐12 and occurred predominantly in poorly differentiated (G3) and advanced (T3‐T4) tumors. Int. J. Cancer (Pred. Oncol.) 89:194–197, 2000. © 2000 Wiley‐Liss, Inc.