Between February, 1983 and August, 1987, twelve children, aged from 2 years to 16 years, underwent aortic valve replacement associated with enlargement of aortic annulus successfully. According to the form of the left ventricular outflow tract obstruction, enlargement of aortic annulus was performed by Konno procedure in eight cases, by Nicks procedure in three cases and by Manouguian procedure in one case. In Manouguian procedure, mitral valve replacement associated with enlargement of mitral annulus was carried out simultaneously. In Konno and Manouguian procedures, the diameter of aortic annulus was enlarged from 180% to 200% compared with the original annular size, whereas in Nicks procedure, the diameter was enlarged around up to 110%. St. Jude Medical valve, of which size ranged from 21mm to 25mm, was employed in these procedures. All these children survived operation, and the post-operative follow up period ranged from 1 month to 55 months. There was one late death eleven months after Konno procedure because of respiratory failure resulting from pulmonary hypertension which persisted postoperatively. The remaining eleven children are surviving well after procedure. These results suggest that aortic valve replacement associated with enlargement of aortic annulus is an acceptable procedure in children with small aortic annulus or sub-aortic stenosis.