The mitral valve was approached through a vertical transeptal incision extended into the roof of the left atrium in 111 patients. Good exposure was invariably provided even in unfavorable situations such as a small left atrium combined with right ventricular hypertrophy or a previously implanted aortic prosthesis. The only hospital death in the entire series was not related to this approach to the mitral valve. Due to breakage of the suture in the roof of the left atrium and to incomplete reconstruction of the atrial septum resulting in a large left-to-right shunt, 2 patients required reinstitution of cardiopulmonary bypass. Both had a smooth postoperative course. Other intra- or postoperative complications related to the incision did not occur. Duration of cardiopulmonary bypass and aortic occlusion was not significantly different from that of patients operated upon through the conventional left atrial approach in the year preceding the experience embraced by this study. Only 3 of 52 patients who were preoperatively in sinus rhythm were discharged in atrial fibrillation. Enhanced atrial vulnerability was demonstrated preoperatively in all 3. These data support a wide application of the extended vertical transeptal approach in mitral valve surgery.