An important application of the renal ultrasonography is to characterize mass lesions of the kidney. It isbecoming increasingly apparant, that gray scale ultrasonography can and should play a primary diagnostic role inpatients with renal mass lesions. Authors analyzed 37 cases of ultrasonography of patients with renal masslesions, from March-15-'79 to Jan-31-'80, at the department of Radiology, Seoul National University Hospital. Theresults are as follows; 1. 11 cases of solid renal tumors(8 renal cell cancer, 1 wilms' tumor, 1 angiomyolipoma, 1transitional cell cancer) show internal echoes and weaker distal-wall echoes, due to sound absorption through themass. No solid masses were diagnosed as cystic disease by ultrasonography. 2. All cases of the renal cysts(15cases ) show sharply defined echo-free zone having strong far-wall echoes. 3. 10 cases of polycystic diseasereveal bilateral enlarged kidneys replaced by multiple cystic structuresof varying size, and concomittentinvolvment of the liver is seen in 4, cases.