p57Kip2 (or CDKN1C) is a potent tight-binding inhibitor of several G1 cyclin complexes and is a negative regulator of cell proliferation. The gene encoding human p57Kip2 is located on chromosome 11p15.5, a region implicated in both sporadic cancers, Wilm’s tumor, and Beckwith-Wiedemann syndrome (BWS), a cancer syndrome, making it a tumor suppressor candidate. BWS is characterized by numerous growth abnormalities and an increased risk of childhood tumors. Several types of childhood tumors, including Wilms’ tumor, adrenocortical carcinoma, and rhabdomyosarcoma, display a specific loss of maternal 11p15 alleles, suggesting that genomic imprinting plays an important part. This region also contains two other imprinted genes, insulin-like growth factor II (IGF-II) and H19, both of which seem to be implicated in adrenal neoplasms.