Coronary arteries in truncus arteriosus. The origin and distribution of the coronary arteries was described in 39 autopsy specimens of truncus arteriosus (TA). The specimens were classified according to the number and the patterns of the truncal cusps. The position of the truncal cusps was defined in relation to intracardiac structures, namely, the atrioventricular orifices. Bicuspid truncal valves were observed in 8 cases (21%), tricuspid in 22 cases (56%) and quadricuspid in 9 cases (23%). All tricuspid valves had 2 anterior and 1 posterior cusp. Great variability in the origin of the coronary arteries was observed, with a tendency for the right coronary artery to arise from the anterior right quadrant and for the left coronary artery to arise from the anterior and left quadrant. Such a tendency was observed in 50% of the bicuspid, in 59% of the tricuspid and in 66% of the quadricuspid valves. The anatomic right ventricle was always observed to be vascularized by a right coronary artery, and the anatomic left ventricle by a left coronary artery, even in cases in which there was a single coronary trunk. The anterior surface of the right ventricle was crossed by a right coronary artery in 5 cases. A single coronary artery was observed in 7 cases (18%). Embryologic considerations are offered, especially regarding the relation between the observed variability in coronary artery patterns in TA and the absence of the truncal septation. 