It has been hypothesized that abdominal trauma may be one of the factors involved in membranous obstruction of the inferior vena cava. We present two cases of membranous obstruction of the inferior vena cava associated with trauma. One asymptomatic case, associated with an occult myeloproliferative disorder, developed within 3 years of a violent abdominal trauma. The other case, associated with familial plasminogen deficiency, was discovered at surgery 3 days after a road accident with obvious abdominal trauma, since superimposed extensive thrombosis of the inferior vena cava caused acute Budd-Chiari syndrome. We conclude that underlying prothrombotic conditions are probably necessary for the development of membranous obstruction of the inferior vena cava and that minor trauma may contribute to the development of thrombosis through indirect mechanisms.