We report two cases of lower extremity venous pathology mimicking deep vein thrombosis (DVT). The first case was a 20-year-old male with swelling in the left leg. Colour Doppler ultrasound (CDUS) demonstrated a continuous flow pattern, and computed tomography (CT) revealed compression of the dilated left common iliac vein by the right common iliac artery (May-Thurner syndrome). This dilatation of the vein was caused by overload due to the drainage of the gluteal arteriovenous malformations into this vein. The second case was a 55-year-old female with swelling and pain of the left leg persisting for a year following an operation of a herniated lumbar disk. She was diagnosed as DVT and treated accordingly. Control CDUS performed in our department demonstrated a left iliac arteriovenous fistula and a pulsatile flow pattern in the left femoral vein. CT also confirmed this arteriovenous fistula. We suggest that if not all criteria for the diagnosis of DVT are fullfilled by CDUS, another imaging modality such as multidetector CT should be used.