The clinical efficacy of thromboprophylaxis with aspirin and dextran 40 was compared in a prospective review of 530 geriatric hip fracture patients treated surgically. All patients were also treated with early mobilization with weight bearing as tolerated and above-knee elastic stockings. In addition to clinical efficacy in preventing thromboembolic complications [deep vein thrombosis (DVT), pulmonary embolism (PE)], safety and cost-effectiveness were also assessed. The overall incidence of clinical thromboembolic disease was 2.8% (DVT = 0.4%, PE = 2.4%). The incidence of DVT (0.5%) and PE (2.6%) in the aspirin group was essentially the same as the incidence of DVT (0.3%) and PE (2.4%) in the dextran group. The inhospital mortality rate (aspirin 4.6%, dextran 3.8%), wound drainage (aspirin 1.5%, dextran 0.9%), deep wound infection (aspirin 0.5%, dextran 0.3%), gastrointestinal bleeding (aspirin 2.1%, dextran 1.5%), and congestive heart failure (aspirin 2.6%, dextran 1.8%) did not differ significantly between the two groups. The intraoperative transfusion rate was similar in both groups (aspirin .65 units, dextran .55 units). However, postoperatively, the transfusion rate was significantly higher in the dextran group (aspirin .26 units, dextran .41 units, p < .05). The treatment of thromboembolic complications was the same for each group and therefore represents similar treatment costs. However, the cost of prophylaxis with dextran was $309 per patient and with aspirin was $1.79 per patient. Our findings suggest that, based on clinical diagnostic criteria, aspirin and dextran are equally effective thromboembolic prophylactic agents in geriatric hip fracture patients. The safety, cost, and ease of administration of aspirin may make its use more desirable.