Our laboratory has found genomic imprinting of a large genomic domain of human 11p15.5, identifying six imprinted genes within this domain: (a) insulin-like growth factor II (IGF-II), an important autocrine growth factor in a wide variety of malignancies; (b) H19, an untranslated RNA that is a putative growth suppressor gene regulating IGF-II; (c) p57KIP2, a cyclin-dependent kinase inhibitor that causes G1-S arrest; (d) KvLQT1, a voltage-gated potassium channel; (e) TSSC3, a gene that is homologous to mouse TDAG51, which is implicated in Fas-mediated apoptosis; and (f) TSSC5, a putative transmembrane protein-encoding gene. We hypothesize that 11p15 harbors a large domain of imprinted growth-regulatory genes that are important in cancer. Several lines of evidence support this hypothesis: (a) we have discovered a novel genetic alteration in cancer, loss of imprinting, which affects several of these genes, and is one of the most common genetic changes in human cancer; (b) we have found that the hereditary disorder Beckwith-Wiedemann syndrome, which predisposes to cancer and causes prenatal overgrowth, involves alterations in p57KIP2, IGF-II, H19, and KvLQT1; (c) we have found both genetic (somatic mutation in Wilms' tumor) and epigenetic alterations (DNA methylation) in cancer; and (d) we can partially reverse abnormal imprinting using an inhibitor of DNA methylation. We propose a model of genomic imprinting as a dynamic developmental process involving a chromosomal domain. According to this model, cancer involves both genetic and epigenetic mechanisms affecting this imprinted domain and the genes within it.