OBJECTIVE: To compare the use of healthcare services in patients receiving enoxaparin, a low molecular weight heparin versus those receiving unfractionated heparin as prophylaxis against deep-vein thrombosis (DVT) following total hip replacement surgery. DESIGN: Economic evaluation undertaken in conjunction with a randomized, open-label, parallel group, Phase III clinical trial. SETTING: 32 US acute-care hospitals. PATIENTS: 607 patients undergoing elective total hip replacement. INTERVENTIONS: Enoxaparin 30 mg q12h, enoxaparin 40 mg qd, or unfractionated heparin 5000 units q8h started within 24 hours following surgery and continued for 7 days. MAIN OUTCOME MEASURE: (1) Use of selected tests and treatments for DVT; (2) use of selected tests and treatments related to post-operative bleeding; (3) length of stay in hospital; and (4) readmissions to hospital within 14 days. RESULTS: Although the use of selected tests and treatments related to DVT or postoperative bleeding did not differ significantly between the three treatment groups, mean length of stay in the hospital (following the start of study therapy) was shorter among patients receiving enoxaparin 30 mg (9.5 days; p=0.01) or 40 mg (9.9 days; p<0.05) than those receiving unfractionated heparin (11.3 days). There was also a trend toward fewer hospital readmissions in both of the enoxaparin groups. CONCLUSIONS: Compared with unfractionated heparin, use of enoxaparin following total hip replacement may decrease the risk of DVT and length of hospital stay.