Recent molecular studies have revealed that a 22q11 deletion is frequently detected in DiGeorge syndrome (DGS), velo-cardio-facial syndrome (VCFS), and conotruncal anomaly face syndrome (CTAFS). As one of the major clinical manifestations in these three syndrome is conotruncal cardiac malformation, we prospectively studied the frequency of a 22q11 deletion in a group of patients with conotruncal cardiac malformation. Fluorescence in situ hybridization (FISH) analyses using N25 (D22S75) DiGeorge Chromosome Region probe were performed on 64 patients with conotruncal cardiac malformation, who visited our clinic from October 1993 to January 1994. Of the 64 patients studied, a 22q11 deletion was detected in 5 patients (7.8%): 3 out of 30 patients with tetralogy of Fallot, one of three with interruption of the aortic arch, and one hemitruncus patient. No deletion was found in 16 patients with complete transposition of the great arteries, 8 with double outlet right ventricle and 2 with aortopulmonary window. In these five patients with 22q11 deletion, patient 1 was clinically diagnosed as having DGS, patients 2 and 3 had CTAFS, and patient 4 had VCFS. Patient 5 could not be dysmorphologically evaluated. It was noteworthy that all patients with a 22q11 deletion, except a non-evaluated patient, had some symptoms DGS, CTAFS or VCFS, and that we failed to identify a non-syndromic 22q11 deletion positive patients in the present series' of 64 patients. Conclusion. This study suggests that it is advisable to bear 22q11 deletion in mind when a patient with conotruncal cardiac anomalies has some other features of DGS, VCFS or CTAFS.