Two fetuses of approximately 11 weeks development with aplasia of the pulmonary as well as the aortic valve leaflets are reported. Both cases showed additional cardiac malformations. Case 1, with all leaflets missing, also had double-outlet right ventricle, hypoplastic left ventricle, large ventricular septal defect, straddling tricuspid valve, and atretic mitral valve. Case 2, with only one hypoplastic aortic valve leaflet, showed hypoplasia of the mitral valve and the left ventricle, and a subaortic ventricular septal defect. The observations made and data in the literature suggest that aplasia of semilunar valve leaflets reflects an underdevelopment of the endocardial cushion swellings at the ventriculoarterial junction, rather than resulting primarily from a malseptation of the cardiac outflow tract.