The Authors summarize their 5-year experience of the clinical use of the Sorin tilting disc prosthesis in 40 patients (group A) with narrow aortic annulus, compared with a control group (group B: 116 patients) where a larger Sorin prosthesis was implanted. Follow-up lasted from 1 to 60 months, with a mean of 25.6 +/- 12.3 in group A and 20.4 +/- 11.9 in group B. Early and late mortality were low: 1/40 and 2/39 (2.5 and 5.1%) in group A and 4/116 and 9/112 (3.4 and 8.0%) in group B (p = NS): only two deaths, one in each group, were prosthesis-related. Actuarial survival was comparable: 91.2% (CL: 96.3-86.1%) in group A and 78.0% (CL: 87.6-68.4%) in group B, as were probability of being event-free and alive, non-reoperated and with few or no symptoms [group A: 61.7% (CL: 72.4-51.0%) and 77.4% (CL: 85.9-68.9%) respectively; group B: 78.8% (CL: 83.4-74.2%) and 61.1% (CL: 85.9-68.9%) respectively]. The Authors conclude that the Sorin tilting disc prosthesis is a reliable valve substitute in the narrow aortic annulus; they recommend that enlargement procedures should be confined only to patients with annulus size less than 19 mm.