Sirolimus is an immunosuppressant mostly used for the management of kidney transplant recipients. This drug by very specifically and effectively inhibiting mTOR, exerts antiproliferative and growth inhibiting effects that might serve preventing uncontrolled tubular cell proliferation and could be extremely important for the inhibition of cyst progression in APKD. Interestingly, studies in rat models of ADPKD have shown that short-term treatment with sirolimus resulted in dramatic reduction of kidney size, prevented the loss of kidney function, and lowered cyst volume density. Similarly, retrospective observations from kidney transplant recipients have documented that sirolimus treatment reduced kidney volumes by 25%, whereas there was no effect in patients not given the drug.