Long-term follow-up, cardial complications and factors influencing the survival time have been investigated retrospectively in 503 patients, who underwent 344 aortic and 191 mitral valve replacements with Björk-Shiley heart valve prosthesis between 1973 and 1984 at the University Hospital of Berne, Switzerland. Informations were assessed from the patient's files and a questionnaire to the family physician. The cumulative follow-up contains a total of 4,810 patient years or a median of 14 years per patient. The median survival time was 19 years, hardly less than the normal life expectancy. Of the 135 patients found alive in 1996 66% had no cardiac problems at all. Two cases of outlet strut fracture of the Björk-Shiley valve were reported during the follow-up time. Both patients had a mitral valve replacement in 1982 with a 31 mm Björk-Shiley valve because of mitral stenosis. The most common complication was a thromboembolic incident (1.6 in 100 patient years). Furthermore eight cases of valve thrombosis, 16 of endocarditis and 24 of myocardial infarction occurred in this population. The study showed that survival time after heart valve replacement with Björk-Shiley valve is long. The mortality was elevated significantly with the following preoperative findings: severe dyspnea (x 2.0), pulmonary congestion (x 1.7) and increased cardiac size (x 1.5). The survival time was shorter when a valve prosthesis with a diameter larger than 27 was used or when in addition coronary heart disease, hypertension, diabetes mellitus or obesity were present.