Abstract: To investigate if microdeletion of chromosome 22q11 is an epidemiologically important cause of congenital heart disease (CHD), we studied 25 cases with CHD phenotypes. Venous blood samples were tested by fluorescence in situ hybridization (FISH) for microdeletion of 22q11. Among 23 cases with simple CHD, 19 were shown not to have microdeletion of 22q11 and the other 4 cases were shown to have 22q11 microdeletion. Microdeletion of 22q11 was found in 2 cases with Tetralogy of Fallot (TOF) accompanied by multiple malformations. The results suggested that microdeletion of 22q11 was associated with CHD.