Intrarenal anatomy including cortex, medulla, and arcuate vessels can be demonstrated with gray scale ultrasonography by using higher frequencies, appropriately focused transducers, and simple sector scans. We have defined this anatomy in three cadaver kidneys, in in vivo normotopic and transplanted kidneys, and in a fetal kidney in utero. The normal cortex is echogenic. The normal medulla is sonolucent and has a characteristic appearance distinguishing it from renal cystic disease. The arcuate vessels can be recognized as a discrete high level echo at the corticomedullary junction and serve as a marker for the evaluation of renal cortical thickness. The ability to identify and characterize intrarenal anatomy should aid in the discovery of smaller renal lesions and in the diagnosis of medical renal disease.