Clinical presentation of unilateral renal cystic disease (URCD) is characterized by multiple simple cysts in only 1 kidney. Involvement of other intra-abdominal organs is not found. Renal function is usually preserved despite the existence of multiple cysts. No genetic background can be delineated up to the present. We present 1 patient with URCD, who was evaluated for his right flank pain. Urinalysis and biochemical tests showed normal renal function (BUN 5.03 mmol/l, creatinine 110.5 micromol/l). Ultrasonographic examination was done and it revealed 2 right renal stones. Furthermore, multiple renal cysts over the juxta-medullary area were noted. His left kidney was intact. Computed tomography (CT) of both kidneys confirmed this finding. 99mTc-DTPA renal scan showed that the glomerular filtration rate of both kidneys was not significantly different. There was no family history of renal diseases. His parents, grandparents and siblings were examined for possible kidney lesions, but none of them had any renal cystic lesion. This patient was followed for only a relatively short period of time (3 years) and his renal function did not deteriorate. Follow-up image studies with sonography and CT were not different from the previous ones.