The likelihood of a paternally expressing imprinted gene in chromosome region 6(q23-24) has been highlighted by cases of transient neonatal diabetes mellitus (TNDM) in which paternal uniparental disomy (UPD) for chromosome 6 or paternal duplication 6(q23-qter) was detected. We present the case of a 38-year-old man with moderate to severe intellectual delay, short stature, small hands and feet, eye abnormality, small mouth, and obesity (without hyperphagia) beginning in mid-childhood. The perinatal and neonatal histories were normal. The patient had a duplication within 6q. Fluorescence in situ hybrisation studies were performed with single and dual hybridisations using a chromosome 6 library probe, short and long arm subregional probes, 6q23-24, 6q25.3-6qter locus-specific probes, and a 6q telomere probe. The hybridisation results defined an inverted duplication of 6q24.3 to 6q27. DNA studies with microsatellite markers from 6p and 6q showed regular biparental inheritance of chromosome 6 and confirmed that the duplication was paternal in origin. Our patient appears to be the first one known to have paternal duplication of chromosome area 6(q24-q27) who did not have TNDM as an infant. He has remained nondiabetic, although obesity, without hyperphagia, has been a constant problem since its onset in mid-childhood. Am. J. Med. Genet. 84:125-131, 1999.