Four cases of "absent pulmonary valve" (APV) are described. This congenital heart disease consists of aplasia or extreme hypoplasia of pulmonary semilunar cusps and is always combined with aneurysmatic dilatation of pulmonary artery. In two of them the diagnosis was confirmed at autopsy. The remaining two are clinical reports surgically confirmed. One of them was studied by single cristal and two-dimensional echocardiography. In three cases APV was associated with tetralogy of Fallot, while in one case there was an intact ventricular septum. Review of literature allowed us to select 149 cases of APV anatomically confirmed, besides our ownes. It is stressed on that APV is usually associated with dextroposition of the aorta and ventricular septal defect by conoventricular malallignment. It is suggested that pathogenesis of this malformation is a consequence of an anomalous development of mesenchimal tissue of pulmonary cusps rather than an asymmetrical truncal sepimentation. We favour the hypothesis that aneurysmatic dilatation of pulmonary artery is caused by altered hemodynamics acting both in foetal and extrauterine life, even if differently expressed. Pathophysiologic and diagnostic value of cyanosis, dyspnea, and systo-diastolic murmur are discussed. Some outlines of the most important diagnostic procedures are reviewed and particularly echocardiography, which shows aortic overriding and dilatation of right ventricular outflow tract and pulmonary artery separated by a restricted pulmonary annulus. Prognosis and therapy are also mentioned.