Truncus arteriosus is characterized by a single arterial vessel arising from the base of the heart and giving origin to the systemic. pulmonary and coronary circulation, To evaluate the incidence, types, and associated anomalies, 18 cases of truncus arteriosus diagnosed by angiocardiography, were reviewed and were compared with other reports, ten of them were confirmed by operation. The overall incidence of truncus arteriosus was 0.127%. Accordin to Collett and Edwards classification, type I was encountered in 11 cases (61%), type II in 4 cases (22%) and type III in 3cases (17%) All the patients had subtruncal ventricular septal defects. Eight pateints showed truncal valve regurgitation and valve stenosis was noted in one case. A right aortic arch was present in 9 cases. Associated anomalies were atrial septal defect(8cases). patent ductus arteriosus(3 cases). coarctation of the aorta(2 cases). isolation of the left subclavian artery (2 cases) and right aortic arch with an aberr nt left subclavian artery( 1 case). Truncus arteriosus is an uncommon congenital cardio vascular malformation. In the group of cases which we encountered. type 1 was the most common anomaly. Frequently associated anomalies were right aortic arch. in-competent truncal valve and atrial septal defect.