Epigenetic lesions are common in neoplasia and range from hypermethylation of subsets of CpG islands to loss of imprinting. By exploiting an episomal model system and the strong de novo methylation capacity of a human cancer cell line, we show that an H19 minigene rapidly becomes methylated and silenced, mimicking the inactivation of the maternal H19 allele in a range of cancers. Although the H19 imprinting control region (ICR) initially displayed methylation protection, it eventually succumbed to the pressure mounted by the de novo methylation machinery of the JEG-3 cells. Importantly, we were able to visualize the kinetics of the loss of the H19 ICR chromatin insulator function in association with chromatin compaction. Our results document that a strong de novo methylation machinery leads to loss of methylation privilege states of H19 ICR to functionally manifest loss of insulator function in a matter of only a few days in human cancer cells.