In a retrospective analysis, comparison was made between the Cutter-Smeloff ball valve (n = 63) and the Lillehei-Kaster tilting disc valve (n = 256) in the aortic position. No significant intergroup difference was found as regards rate of thromboembolism (0.6/100 patient years for both valve types), endocarditis (0.2 for Cutter-Smeloff and 0.5 for Lillehei-Kaster/100 patient years) and paraprosthetic leak (0.9 and 0.5, respectively/100 patient years). The actuarial curve of cumulative survival was similar for both valves until 6 years postoperatively. Thereafter the outcome was less favourable for the patients with Cutter-Smeloff valve (actuarial survival 79 +/- 5% than for those with Lillehei-Kaster valve (91.2 +/- 2%). The reason for this, statistically significant, difference may be associated with the difference in valve profiles.