PURPOSE: This study was undertaken to determine the incidence of chromosome 22q11 deletion in patients with infundibular ventricular septal defect(VSD). METHODS: Sixty-two children with infundibular VSD were included in this study from January 1999 to December 2000. Chromosome 22q11 deletion was confirmed by FISH, using LSI DiGeorge/VCFS region dual color probe(Vysis, USA). RESULTS: Thirty-two patients had conotruncal cardiac defects:tetralogy of Fallot (TOF) in 15; TOF with absent pulmonary valve in 1; VSD with pulmonary atresia in 7; truncus arteriosus in 3; double outlet right ventricle in 2; interrupted aortic arch in 2; transposition of the great arteries in 2. Thirty patients had isolated infundibular VSD without conotruncal cardiac defect:perimembranous infundibular VSD in 15; subarterial infundibular VSD in 9; muscular infundibular VSD in 6. Chromosome 22q11 deletion was observed in 8 patients(male 5, female 3):TOF 2; VSD with pulmonary atresia 4; truncus arteriosus 1; perimembranous infundibular VSD 1. All of the patients with chromosome 21q11 deletion showed typical facial appearance. Low incidence was found of chromosome 22q11 deletion in patients with infundibular VSD without conotruncal cardiac defect than in those with conotruncal cardiac defect(3.3% vs 21.9%). CONCLUSION: These data indicate that a small proportion of isolated infundibular VSD is pathogenetically related to deletion of chromosome region 22q11.