A 22-year-old woman had been treated with a Ross operation for aortic root aneurysm and aortic regurgitation 10 years previously. In the initial Ross operation, a handmade tri-leaflet conduit was used for the right ventricle outflow tract (RVOT) reconstruction. The conduit was prepared preoperatively, by sewing a folded 0.1 mm expanded polytetrafluoroethylene (ePTFE) membrane onto the luminal cavity of the 24 mm woven double velour vascular graft, thereby creating a tri-leaflet valve. During ambulatory follow up after discharge, dilation of the pulmonary autograft had been observed, and its maximal diameter reached 60 mm. Furthermore, preoperative a pressure study revealed a 25 mmHg pressure gradient between the right ventricle and the pulmonary artery. At the time of reoperation, we performed an aortic root replacement combined with RVOT conduit replacement. A 24-mm woven double velour vascular graft integrating a 21-mm On-X mechanical prosthesis was used for aortic root replacement. A handmade ePTFE tri-leaflet conduit, 26 mm in size, was used to replace the previous RVOT conduit. The operation was successful, and the postoperative course was uneventful. The explanted conduit was sent for microscopic examination, which revealed that the graft was covered by a fibrocollagenous membrane. On the contrary, no surface membrane was found on the ePTFE valve. Moreover the microscopic examination showed cystic medionecrosis of the pulmonary autograft. Both dilatation of the pulmonary autograft and RVOT conduit failure were successfully treated at the second operation. However this young patient will require follow-up of the mechanical prosthesis and RVOT conduit for the rest of her life.