The point prevalence and clinical significance of renal vein thrombosis (RVT) was evaluated in 27 of 33 consecutive nephrotic patients with idiopathic membranous glomerulopathy. A technique of retrograde venography after the injection of epinephrine into the main renal artery to decrease renal blood flow was used. Two patients had histories compatible with a thromboembolic event, and the excretory urogram was not suggestive of RVT in any patient. RVT was noted in 13 patients; in eight it was bilateral. All patients with RVT received anticoagulant drugs for a minimum of 1 year after the study, and no thromboembolic events occurred in this group. No patient was treated with corticosteroids. Follow-up observation of an average of 2.5 years has not revealed a significant difference in the rate of renal function deterioration or change in degree of proteinuria between patients with and without RVT. Coagulation abnormalities included elevated platelet counts and plasma fibrinogen levels and prolonged reptilase and thrombin times. These were noted in all 14 patients studied, six of whom had RVT. In patients experiencing a nephrotic remission, coagulation abnormalities reverted to normal. RVT is common in idiopathic membranous glomerulopathy with nephrosis and is associated with few clinical markers. Its influence on renal function and proteinuria is of questionable significance. Coagulation abnormalities may be a causative factor of RVT in this setting.