Patients with warfarin-related nephropathy present with an acute rise in serum Cr after becoming supratherapeutic on warfarin therapy (INR>3). The renal biopsy findings of warfarin nephropathy include acute tubular injury, occlusive RBC casts in tubular lumens, and RBCs in Bowman’s space. The diagnosis of warfarin nephropathy cannot be made exclusively on biopsy and requires clinical correlation as other glomerulonephritides can have similar changes. Nevertheless, the renal pathologist should suspect warfarin nephropathy when the number of RBC casts is disproportionate to the degree glomerular injury (e.g. mild mesangial immune complex deposition without proliferative changes yet there are numerous RBC casts).