Interstitial duplications of 11q are very rare and seldom reported. In this paper we describe the first case of a duplication involving bands 11q11 and 11q12. This newly described patient has multiple craniosynostoses, congenital heart defect and developmental delay, and is a carrier of a mosaic duplication: 46,XY,dup(11)(q11→q13.3)(29)/46,XY(6). The breakpoints were further delimited by comparative genomic hybridization microarray. We also performed fluorescent in situ hybridization analysis to determine the extension of the duplication in a patient described earlier with a duplication 11q13.5–q21. An overlapping region of less than 1.2 Mb was identified and included the duplication of genes FGF3 and FGF4 in both individuals. We discuss the possible implications of dosage effects of these genes in the onset of craniosynostosis. © 2007 Wiley-Liss, Inc.