In contrast with extensive information on the management of deep vein thrombosis of the lower extremities, little is known on the most appropriate treatment of the superficial vein thrombosis (SVT). In a multicenter, prospective, controlled, double-blind, double-dummy clinical trial, 164 consecutive patients with acute SVT of the great saphenous vein were randomized to receive the s.c. administration of either fixed prophylactic doses (2850 a-Xa IU) or body-weight adjusted therapeutic doses of nadroparin once daily for 1 month. The main study outcome was to compare the rate of asymptomatic and symptomatic extension of SVT and/or venous thromboembolic (VTE) complications during a 3-month follow-up period. Of the 81 patients randomized to the prophylactic doses, seven [8.6%; 95% confidence interval (CI), 3.5-17.0] developed SVT progression or VTE complications as compared with six of the 83 (7.2%; 95% CI, 2.8-15.1) allocated to the treatment group (absolute difference, 1.4; 96% CI, -6.9 to 9.7; P = 0.74). No patient in either group developed major bleeding. Our findings suggest that therapeutic doses of low-molecular-weight heparin, administered for 1 month in patients with SVT of the greater saphenous vein do not improve results obtained by prophylactic doses, administered for the same period, over a 3-month follow-up period.