PURPOSE: The risk factors and clinical characteristics in young patients with deep venous thrombosis (DVT) were analyzed. METHOD: The clinical characteristics of the 118 patients registered at our DVT clinic, from September 2000 to August 2002, were retrospectively reviewed. Information reviewed included sex ratio, site and extent of DVT, frequency of pulmonary embolism (PE), recurrence rate, and thrombophilic states. The patients were dichotomized into two groups according to their age, less than 40 years vs. older than 40 years. Their risk factors were also analyzed according to "Reporting Standards in Venous Disease". RESULT: Among 118 patients, 48 (40.7%) were younger than 40 years. Right leg DVT was more common (37.5% vs. 18.2%) in the younger group although the more common site for DVT was in the left leg. Also, PE (14.6% vs. 10.0%) and mesenteric venous thrombosis (14.6% vs. 4.3%) were more common, with higher recurrence rates (35.4% vs. 21.4%), in the younger group. However, there was no significant difference. Except for age or pregnancy and postpartum state, mean total scores of risk factors were higher in the older group (1.06 vs. 1.77). On the contrary, positive family history of DVT (10.4%) was found only in the younger group. Thrombophilic states, including antithrombin III, protein C, and protein S deficiencies, and Behcet's disease were more prevalent in the younger group whereas activated protein C resistance was found more often in the older group. In patients who had thrombophilic states, recurrence rate of DVT was much higher. CONCLUSION: For proper diagnosis and management of young DVT patients, especially to prevent a disastrous PE and recurrence, we must make efforts to identify risk factors including thrombophilic states.