Simple cyst of the kindey is usually unilateral and single and usually involves the lower pole of the kidney. Although many of them are benign, a few have a tendency to become malignant. Asymptomatic simple renal cyst lies in the diagnostic delemma of determining whether the mass lesion is a cyst or a renal carcinoma. With the advent of many new diagnostic procedures, the diagnosis of renal cysts reaches 98% of accuracy. Authors experienced one case of simple renal cysy involved the upper pole of the right kidney in 48 year old female, and report this case with the review of literatures