Seventeen women with thrombosis during pregnancy were studied prospectively. The deep venous thrombosis (DVT) was diagnosed objectively with phlebography, plethysmography and thermography. In many cases (13/17) the dominant symptom was diffuse pain in the lower abdomen and/or leg which in several cases caused a delay in the diagnosis. The traditionally typical thrombotic signs were often missing. Proximal thrombi were predominant (13/17) as were left-sided ones (14/17). During pregnancy and lactation the patients were treated with heparin which, after the initial parenteral administration, was given subcutaneously by self-administration. In conclusion, DVT must be suspected and non-invasive diagnostic tests be liberally performed in cases of uncharacteristic lateral and/or declive abdominal pain or leg pain during pregnancy. The DVT must always be objectively verified before treatment. In patients with pregnancy DVT there is no indication for early labor induction and the patients can be delivered by the normal vaginal route. It is recommended that patients with DVT during pregnancy should be treated with heparin subcutaneously which can be self-administered. The post-partum treatment may be continued for 2-3 months with heparin subcutaneously or peroral anticoagulants.