Beckwith-Wiedemann syndrome (BWS) is a congenital disorder of imprinting caused by epimutations and mutations affecting two imprinted loci on chromosome 11p15. Its clinical features are heterogeneous, including macrosomia, macroglossia, hemihyperplasia, abdominal wall defects, neonatal hypoglycemia, and increased risk of embryonal tumors such as Wilms tumor, adrenocortical carcinoma, hepatoblastoma, and neuroblastoma. The molecular and clinical heterogeneity of BWS makes the diagnosis challenging, but essential, since different etiologies of BWS have different clinical prognoses - most crucially, patients with gain of maternal methylation at imprinting control region type 1 (ICR1) are at significant risk of Wilms tumor or hepatoblastoma. We present three cases of BWS with different symptomatology and two different molecular diagnoses. The authors emphasize the importance of molecular studies in the long-term follow-up of children with BWS, including refinement of phenotype-genotype correlation and its connection with optimal management and tumor surveillance.