Patients undergoing abdominal surgeries face substantial risk of experiencing venous thromboembolic events in the perioperative period. The low-molecular-weight heparin dalteparin sodium is clinically effective in reducing the incidence of venous thromboembolism (VTE) in these patients. Dalteparin may be used in low (2500 units [U]) and high (5000 U) once-daily doses for this indication. However, the cost effectiveness of dalteparin 5000 U compared with dalteparin 2500 U and unfractionated heparin (UFH) for this indication has not been studied. To conduct a cost-utility analysis to evaluate the cost effectiveness of dalteparin compared with UFH for preventing VTE in patients undergoing elective abdominal surgery. A Markov model, from a healthcare perspective, was constructed to evaluate the cost effectiveness of dalteparin 5000 U and dalteparin 2500 U compared with UFH. A 69-year-old mixed sex patient population was studied using pooled probabilities of clinical outcomes from randomised, controlled trials. Cost data were mostly derived from Medicare reimbursement, in year 2002-03 values. Cost effectiveness was measured as cost per QALY gained over the patient's lifetime. Total costs for patients given UFH, dalteparin 2500 U and dalteparin 5000 U were US45,855 dollars, US45,882 dollars and US46,308 dollars, respectively, while QALYs were 9.5603, 9.5632 and 9.5811, respectively. Hence, the incremental cost effectiveness of dalteparin 5000 U over dalteparin 2500 U and UFH was US23,799 dollars/QALY and US21,779 dollars/QALY gained, respectively. Similarly, cost effectiveness for dalteparin 2500 U over UFH was US9310 dollars/QALY gained. Univariate sensitivity analysis showed that dalteparin 5000 U maintained its cost effectiveness (incremental cost-effectiveness ratio [ICER] or =90% patients receive the benefit of the medication, policy makers would need to commit substantially more resources than suggested by the baseline ICERs.