along with other distinctive characteristics like asymmetry of body and limbs, craniofacial features, and 5th finger (F5) clinodactyly. Beckwith-Wiedemann syndrome (BWS, OMIM: 130650) is also a growth-affecting disorder which causes overgrowth with many additional clinical features like macroglossia, organomegaly, and increased risk of childhood tumors [Weksberg et al., 2010]. The most common molecular cause for both syndromes is an abnormal regulation of genes in chromosomal region 11p15 [Gicquel et al., 2005], where 2 imprinting control regions (ICR1 and ICR2) control fetal and postnatal growth. ICR1 contains the maternally expressed H19 gene and the paternally expressed IGF2 gene, whereas ICR2 contains the maternally expressed KCNQ1 and CDKN1C genes and the paternally expressed KCNQ1OT1 gene. Normally, genes that are expressed in 1 allele are imprinted (methylated) and silenced in the other allele. Imprinting disturbances lead to abnormal expression of these genes and the clinical phenotypes of SRS or BWS. Approximately 40% of SRS patients show hypomethylation of ICR1, whereas up to 50% of BWS patients have ICR2 hypomethylation [Eggermann et al., 2008]. In addition, in SRS and BWS patients, numerous submicroscopic chromosomal disturbances have been described, among them duplications, deletions, inversions and/or translocations affecting chromosome 11p15 [Begemann et al., 2012;Fokstuen and Kotzot, 2014]. Large duplicaKey Words 11p15 duplication · 11p15 imprinting disorders · Beckwith-Wiedemann syndrome · Imprinting control region 1 · Imprinting control region 2 · Silver-Russell syndrome Abstract Silver-Russell syndrome (SRS) and Beckwith-Wiedemann syndrome (BWS) are 2 opposite growth-affecting disorders. The common molecular cause for both syndromes is an abnormal regulation of genes in chromosomal region 11p15, where 2 imprinting control regions (ICR) control fetal and postnatal growth. Also, many submicroscopic chromosomal disturbances like duplications in 11p15 have been described among SRS and BWS patients. Duplications involving both ICRs cause SRS or BWS, depending on which parent the aberration is inherited from. We describe to our knowledge the smallest familial pure 1.3-Mb duplication in chromosomal region 11p15.5p15.4 that involves both ICRs and is present in 3 generations causing an SRS or BWS phenotype.