We present 2 cases of lower extremity deep venous thrombosis in 2 gypsy adolescents from related families. The patients had low antithrombin activity levels and inherited homozygous antithrombin deficiency was confirmed by molecular analysis (Leu131Phe mutation). One patient had a history of nephrectomy at the age of 9 due to nonfunctioning kidney and 2 siblings died at 4 months of age. His mother had 3 fetal losses in the third trimester. The other propositus had an elder sister who suffered from postpartum deep vein thrombosis and pulmonary embolism. Heterozygous mutation was demonstrated in both parents.