Clinical features and pathologic findings of the kidney in three patients with Takayasu's arteritis and associated nephritis are described. Clinical evidence of renal disease included proteinuria, hematuria, and a reduction of glomerular filtration rate. Renal histology revealed mesangial proliferative glomerulonephritis in one patient and minor glomerular abnormalities in the other two. The clinical course of the glomerulopathy is slow, yet progressive, and the corticosteroid and immunosuppressive therapy appear to delay the progression of the glomerular damage. In one patient in whom repeated examination of the kidney after corticosteroid and immunosuppressive treatment was possible, the glomerular pathology remained unchanged. This report of three patients with Takayasu's arteritis and concomitant nephritis supports the previous speculation of the association between these two conditions. The glomerular, vasculitic, and arteriopathic involvements in these patients may suggest a common immunologic mechanism.