From May, 1974, through December, 1978, 255 mitral annuloplasties have been performed at our institution. Forty-three Carpentier rings and 212 flexible rings were used. Simultaneously, 307 patients with predominant insufficiency were treated with a Hancock bioprosthesis. A critical analysis of the flexible ring group versus the Hancock group is presented: The average ages were 41.3 versus 43.3 years. Preoperatively, 55% versus 60% were in Functional Class III and 9.6 versus 25.4% were in Class IV. The valve lesion was caused by rheumatic disease in 91.2% versus 93.9%. A multiple valve operation was required by 51% versus 60%. There was a significant difference in the operative mortality rates (1.8% versus 11.4%). This difference was maintained for each preoperative functional class and for the isolated and multiple valve groups. There was no significant difference in the late mortality rates (1.4% versus 3.7%). The total actuarial survival rates were of 96.4% and 81% (maximum follow-up times 4.0 and 4.5 years). The incidence of embolism was 2.4% and 4.1% per patient-year, with both groups being subjected to the same anticoagulation policy. The incidence of dysfunctions was equal (3.9% per patient-year). Postoperative hemodynamic evaluation of 72 patients having annuloplasty and 129 patients having Hancock valve replacement showed basal mean transmitral gradients of 10.98 +/- 3.6 and 9.66 +/- 2.73 mm Hg. The average effective orifice areas were 1.93 +/- 0.74 and 2.25 +/- 0.46 cm2. While the bioprosthesis behaves hemodynamically like a flow-related variable orifice, the reconstructed valve orifice is dependent upon its preoperative anatomy. In conclusion, the comparison of flexible ring annuloplasty and Hancock valve replacement for mitral valve disease shows a lower operative mortality for the former and comparable medium-term postoperative course. Since both techniques have a limited durability, longer follow-up periods will soon resolve this controversial issue.