Tetralogy of Fallot (TF) is a congenital conotruncal heart defect commonly found in DiGeorge (DGS) and velo-cardio-facial (VCFS) syndromes. The deletion of chromosome 22q11 (del22q11) is a well established cause of DGS and VCFS, and it has been demonstrated also in sporadic or familial cases of TF. In order to investigate the prevalence of del22q11 in patients with TF, we analyzed the DNA of 137 consecutive patients with syndromic and isolated TF, using the HD7k probe, which detects hemizygosity for the D22S134 locus. Del22q11 has been detected in 11/26 (42%) syndromic patients. Evidence for hemizygosity was obtained in all patients with DGS and in 8/15 patients with VCFS. None of the 107 patients with isolated TF had del22q11. Our experience suggests that children with TF and del22q11 always present major or minor extracardiac anomalies. These features, including subtle facial dysmorphisms, should be checked routinely in patients with TF and other conotruncal heart defects.