Sirolimus is a powerful immunosuppressive drug initially used in kidney transplant patients but now increasingly employed in recipients of other types of solid organ transplants, such as liver, heart, lung, or pancreas. Sirolimus is indicated for rescue therapy and to reduce the toxic side effects of calcineurin inhibitors. However, its use has been associated with an uncommon but important pulmonary toxicity. Reports have described interstitial pneumonitis, bronchiolitis obliterans, organizing pneumonia, and alveolar proteinosis. We present the case of a liver transplant patient with interstitial pneumonitis associated with sirolimus.