To understand genetic events which play a role in the development and/or progression of human endometrial cancer, we studied allelotypes on all autosomal chromosomes, as well as chromosome X, with 42 microsatellite markers and 56 endometrial cancers. The most frequent loss of heterozygosity (LOH) was observed on the long arm of chromosome 10 (14 of 30, 47%), which was commonly detected in grade 1 cancer. We constructed a detailed deletion map and defined two commonly deleted regions in 10q25-q26; one was the 8 cM region between D10S209 and D10S216, the other was the 12 cM region between D10S217 and D10S590. Replication errors at two or more loci were observed in 24 of 56 tumours (43%), suggesting that disruption of the DNA mismatch repair system also plays an important role in the course of endometrial carcinogenesis.