Magnetic resonance venography is a recently developed, noninvasive means of visualizing the proximal veins of the lower extremity and pelvis. Magnetic resonance venography is compared with standard contrast venography in the diagnosis of proximal deep vein thrombosis after total joint arthroplasty. Two hundred seven extremities were evaluated in a blinded study 5 to 7 days after surgery. Standard contrast venography identified 11 proximal deep vein thromboses. Initial interpretations of the magnetic resonance venographies by staff radiologists identified 5 of the proximal vein thromboses (sensitivity 45%). Two patients with negative standard contrast venographies were identified as positive (specificity 99%). A retrospective review of all magnetic resonance venographies by a dedicated magnetic resonance angiographer identified 10 of 11 deep vein thromboses seen on standard contrast venography (sensitivity 91%). Both false negatives were identified as positives. Standard contrast venography remains the gold standard for identifying proximal vein thromboses. Emerging magnetic resonance imaging techniques have created a potential alternative modality by which to identify deep vein thrombosis. The present study suggests that standard contrast venography continues to be the most accurate modality currently available. Although magnetic resonance venography seems to be accurate, its interpretation requires experience. As costs diminish and experience increases, magnetic resonance venography will have increased importance in the clinical recognition of deep vein thrombosis.