We report a boy with duplication of a small segment of the short arm of chromosome 7 (46,XY, dir dup (7) (p21.2-->22.1). The boy presented with supravalvular pulmonary stenosis, atrial septum defect and mental retardation. The origin of the additional material from chromosome 7 was confirmed by fluorescence in situ hybridization. This technique in combination with the use of single-copy DNA probes may in future help to delineate the phenotype/karyotype correlation.