Benign renal cystic adenoma with out malignant features is a very rare entity. A 75 year old male with obstructive Lower tract symptoms and vague flank pain was admitted and planned for nephrectomy of non functional kidney -due to long term nephrolithiasis- intra operative finding was a cystic hydronephrotic kidney filled by thick mucous secretions which turned out to be a cyst adenoma of kidney with no malignant features.