To test for the existence of genomic imprinting in human gynecologic tumors, we analyzed the allelic expression of human insulin-growth factor-II (IGF-II) genes. Genomic imprinting is the parental allele-specific expressions of genes, and recently imprinting of IGF-II gene has demonstrated that parental IGF-II was monoallelically expressed. To study whether IGF-II gene imprinting occurs in human gynecologic tumors, we examined allele-specific expression using an ApaI polymorphism in the 3' untranslated region of IGF-II gene exon 9. We used 19 gynecologic tumor cell lines, and 66 human gynecologic tumors. Four of 19 cell lines (21%) were informative, and three of these four cell lines (75%) revealed loss of imprinting (LOI). For gynecologic tumors, 24 of 66 were informative (36%), and 5 of the 24 (21%) had LOI. We have reported here that the IGF-II gene is expressed biallelically in some gynecologic tumors. We suggest that LOI of the IGF-II gene is involved in the development of some gynecologic tumors.