Renal vein thrombosis is a thrombotic occlusion of one or both renal veins. Its most common cause is nephrotic syndrome, which is a hypercoaguable state though to be due at least in part to loss of the anticoagulant proteins protein C, protein S, and antithrombin III from diffuse protein wasting. It can also be secondary to nearly all other forms of nephrotic syndrome (e.g., minimal chnage disease, FSGS, MPGN) and also lupus nephritis particularly in the setting of a lupus anticoagulant. Renal cell carcinoma is also commonly associated with renal vein thrombosis, and local spread of tumor may also continue into the renal vein clot. A variety of imaging tools (e.g., venography, ultrasound, MRI, etc) are available for diagnosis of renal vein thrombosis but the most common means of diagnosing it currently is a CT scan with iv contrast. Surgical means of evacuating the clot are becoming increasingly rare and the mainstay of therapy involves anticoagulation and correcting the underlying cause (e.g., treating nephrosis with ACE-I/ARB, immunosuppresants as warranted, etc). The idea of giving prophylactic anticoagulation to prevent venous thrombosis in nephrotic syndrome is still a controversial one.