32 cases of venous thrombosis of the lower extremities in young adults under 35, are evaluated. Women are essentially affected (62.5%). The clinical picture and complications do not vary, regardless of age. The left side is affected in 66 p. cent of the cases. Obstetrical causes are the most frequent, especially during the post-partum with Caesarean section as an aggravating circumstance. A protein C deficiency is found in 30 p. cent of the patients, and there is no deficiency in antithrombin III. Among other etiologies, orthopaedic surgery and neurological diseases are incriminated, most of the time.