In a twenty-month period, 396 Medtronic-Hall valves were inserted in 341 patients belonging to a Third World population group. Approximately 20% of the patients were given anticoagulants. The total follow-up period was 353 patient years (mean 13 months per patient). Late valve-related mortality was 3.6% patient years (excluding ring leaks) with a valve failure rate (VFR) of 4.0%/patient year. The incidence of thromboembolic complications was 6.8%/patient year while valve thrombosis occurred in 7 patients (2.0%/patient year). Hemolysis was generally subclinical, but 2 patients without ring leaks required transfusion. The initial late results compare favorably with those of St. Jude Medical valve replacement in a similar population group. The supreme test for any substitute heart valve is its successful application in a third world population group because its inadequacies are highlighted by an increased VFR and morbidity.