We report a 4-year-old boy, a 6-month-old girl, and a 17-week-old fetus all with a chromosomal imbalance derived from a balanced translocation t(13;15)(q34;q26.1) of their father. The boy had a partial trisomy for 15q26.1-qter (46,XY,der(13)t(13;15)(q34;q26.1)) and postnatal overgrowth, as well as craniosynostosis, facial anomalies, and finger joint contractures, while the girl with the same chromosomal aberration did not show overgrowth, although she had similar craniofacial and skeletal abnormalities. The fetus had a partial monosomy for 15q26.1-qter and intrauterine growth retardation (IUGR). Fluorescence in situ hybridization (FISH) analysis with a BAC clone covering the insulin-like growth factor 1 receptor gene (IGF1R) that is located to 15q25-q26 revealed three copies in the boy, one copy in the fetus, and two copies in their phenotypically normal father. Since deletion of IGF1Rhas repeatedly been reported to be associated with IUGR, it is tempting to speculate that the dosage of IGF1R may have determined growth in these children. © 2002 Wiley-Liss, Inc.