An infant boy presented with trigonocephaly, mild craniofacial features, a small VSD, open ductus Botalli (ODB), bilateral hip dysplasia, psychomotor retardation, and hypotonia. The karyotype was 46,XY,del(4)(q34). Unexpectedly, fluorescence in situ hybridization (FISH) studies revealed not only a deletion but also a duplication. The deletion extends from 4qter to 4q34.3 and the duplication from 4q32.3 to q34.3. This is the first description of a deletion inverted duplication 4q. Possible mechanisms we can envision by which this deletion/duplication arose could be a U-type exchange causing end-to-end fusion or a two step event with a paracentric inversion and subsequent cross-over in the inverted segment. This observation suggests that the karyotype of patients with a 4q deletion should be confirmed by molecular cytogenetics. © 2004 Wiley-Liss, Inc.