Despite widespread use of laparoscopic procedures, no adequate data are available to support specific recommendations for venous thromboprophylaxis in patients undergoing laparoscopic surgery. This prospective, randomized trial is the first to be designed to evaluate a regimen of out-of-hospital thromboprophylaxis after laparoscopic surgery. Consecutive patients admitted for laparoscopic surgery were considered for the study. The thromboprophylaxis regimen used for each patient was based on a risk score. Possible thromboprophylactic measures included elastic stockings and pre- and postoperative Dalteparin or early ambulation. At discharge, patients were randomly allocated either to continue Dalteparin for 1 week, or to receive no further prophylaxis. Patients judged to be at low risk were not randomized. Compression ultrasound of the leg veins was performed in all patients 4 weeks after hospital discharge. Fifty-three patients, all with acute appendicitis, were judged to be at low risk of deep vein thrombosis and were not included in the randomized study. The remaining 209 patients fell into two groups: 104 patients received postdischarge Dalteparin and 105 patients did not. The incidence of deep vein thrombosis was 0% (0 of 104) vs. 0.95% (one of 105), respectively (P = 1.00). The risk of postdischarge venous thromboembolism is low in patients undergoing laparoscopic surgery who receive in-hospital thromboprophylaxis. Given this low risk, a clinical trial powered to determine if extending prophylaxis in such patients reduces the risk of clinically apparent deep vein thrombosis would be unfeasibly large.