A new study design was evaluated for the estimation of the incidence of thromboembolic complications, bleeding complications and endocarditis in patients with prosthetic heart valves. Thromboembolism is a serious complication in patients with artificial heart valves. Consequently lifelong anticoagulation therapy is indicated for such patients. In the Netherlands the intensity of the anticoagulation is monitored by a network of regional anticoagulation services. The computerized patient information system of the Leiden anticoagulation service was used for a two year follow-up study of patients with mechanical heart valves. In these years anticoagulation was monitored in 273 patients with a total follow-up period of 442 patient-years. The incidence figures for thromboembolism, bleeding complications and endocarditis were 0.9/100 patient-years, 5.6/100 patient-years and 0.2/100 patient-years, respectively. The findings are similar to those of classical follow-up studies. This method is not suitable for detection of the direct early postoperative mortality or for follow-up of patient with heterografts. We conclude that the detection and follow-up by means of regional anticoagulation service offers an opportunity to investigate patients with mechanical heart valves in an efficient way without notable selection.