The risk of thromboembolic complications in outpatient surgery is regarded as being low. Thromboembolic prophylaxis is seldom administered as a routine. A retrospective study in our outpatient department, based upon patients readmitted for clinical thromboembolism, showed an incidence of deep vein thrombosis of 0.05% (8/1 691) and of pulmonary embolism 0.0006% (1/1 691). None of the patients received prophylaxis for thrombosis, and all operations were performed under regional anaesthesia of the lower extremity. 50% of the operations were performed using a tourniquet. 2/3 of the patients were women and 2/3 were over the age of 50. Operation time was usually 30-45 minutes. Our study indicates that patients undergoing knee arthroscopy, and operations for varicose veins and hallux valgus are at risk of thromboembolism. Prospective studies of these risk groups are necessary to figure out the need for thrombosis prophylaxis.