Cases of renal vein thrombosis following infectious kidney diseases have been rarely described [Siqueira-Filho AG, Kottke BA, Miller WE. Primary inferior vena cava thrombosis: report of nine cases. Arch Intern Med 1976;136:799-802]. There have been few cases of renal vein thrombosis accompanying a xantogranulomatous pyelonephritis and a pyonephrosis. Literature reveals no case of renal vein thrombosis developing secondary to an infected renal cyst [Mitchell DG, Friedman AC, Druy EM, Swanberg LE, Phillips M. Xanthogranulomatous perinephritis: unusual cause of renal vein and vena caval thrombosis. Urol Radiol 1985;7:35-8]. This report presents the first case of unilateral infected renal cyst with thrombosis of the renal vein. © 2005 Elsevier Ireland Ltd. All rights reserved.