Hypertension may be due to either vascular(renal artery stenosis) or nonvascular(urologic) causes in hypertensives with unilateral small kidneys. Generally, the occurrence of hypertension in association with difference in kidney size suggests the presence of prolonged renal artery stenosis. This condition can result in decreased volume of the poststenotic kidney. Another cause of small kidneys is unilateral renal agenesis, renal dysplasia with or without reflux, tubular obstruction, and hydronephrosis. Hypertension can be attributed to abnormal-sized kidneys. Nephrectomy of the small kidney or correction of the stenotic artery normalizes blood pressure.