Above-knee graduated compression stockings are effective in preventing postoperative deep vein thrombosis, but are more expensive and less acceptable than below-knee stockings. One hundred and fourteen patients undergoing major abdominal surgery were randomly allocated to wear above-knee or below-knee graduated compression stockings. Deep vein thromboses were diagnosed by isotope uptake in three of 56 patients (5.4 per cent) in the above-knee group and one of 58 patients (1.7 per cent) in the below-knee group. These differences are not statistically significant. Results suggest that below-knee stockings are as effective as above-knee in the prevention of postoperative deep vein thrombosis.