We previously identified two commonly deleted regions on chromosome bands 10q25-q26 in endometrial cancer: an 8-cM region and a 12-cM region. In the present study, we further studied the 8-cM region with 83 endometrial cancer specimens and 14 microsatellite markers and narrowed it down to a 1-cM region between D10S587 and D10S1723. This result was confirmed by two-color fluorescence in situ hybridization analysis. An association between histopathologically lower grade tumor and allelic loss (P = 0.03 by Fisher's exact test) was also observed. We also constructed a yeast artificial chromosome (YAC) contig and found that one YAC clone, which was 790 kb in size, harbored the whole 1-cM region of common allelic loss.