Acquired renal cystic disease has been associated with the development of renal cell carcinoma in patients on chronic dialysis. The disease has been documented to regress in the native kidney after successful renal transplantation. We report 4 cases of renal cell carcinoma occurring in the native kidney 3 to 8 years after successful renal transplantation. Of these patients 3 also had acquired cystic disease of the native kidney. These 3 cases suggest that the malignant potential associated with acquired renal cystic disease may not be reduced significantly by renal transplantation and that periodic imaging of the native kidney is advisable after transplantation, particularly when the disease is present before transplantation.