A 41-year-old man was admitted to our hospital because of shortness of breath. Two-dimensional transesophageal echocardiography revealed the presence of a horseshoe-shaped unicuspid aortic valve (UAV) with two raphes at 4 and 8 o'clock positions of the aortic leaflet, and prolapse of the noncoronary cusp. Three-dimensional transesophageal echocardiography (3DTEE) clearly showed UAV, and another raphe was observed at the 7 o'clock position of the aortic leaflet. The Bentall procedure was performed, and surgical inspection confirmed the diagnosis of UAV based on the quadricuspid aortic valve. The excised specimen of the aortic valve was remarkably similar to the findings of 3DTEE.