Autosomal dominant polycystic kidney disease (ADPKD) is characterized by the massive enlargement of both kidneys caused by numerous cysts. The cyst formation begins in utero and the continuous growth of cysts leads to compression and destruction of non-cystic renal parenchyma, so that finally a kidney replacement in the 5th to 6th decade of life is necessary. So far there is no therapy that halts disease progression. Animal data show that pharmacological inhibition of a central regulator of cell proliferation, the socalled mammalian target of rapamycin (mTOR), slows disease progression. This overview provides an insight into the disease and the specific mTOR inhibitor sirolimus, which is currently tested in clinical trials.