Tacrolimus is a potent immunosuppressant medication with a low therapeutic index. We report a case of mutism with persistent dysarthria in a patient receiving tacrolimus-based immunosuppression following allogeneic liver transplantation. A 59-year-old female patient with end-stage liver disease secondary to primary sclerosing cholangitis underwent successful allogeneic liver transplantation. The patient was started on tacrolimus for prevention of allograft rejection and subsequently developed complete mutism. Following consultation of the medical toxicology service, tacrolimus was discontinued and the patient's mutism gradually improved. However, the patient still has moderate dysarthria more than 2 years after tacrolimus discontinuation. The Naranjo probability scale revealed a probable adverse reaction of mutism and dysarthria associated with tacrolimus therapy. Mutism is an uncommon complication of calcineurin inhibitors. Both cyclosporine and tacrolimus have been associated with mutism, though mutism may be more common in patients treated with tacrolimus. The mechanism of injury has not been delineated, although liver transplant patients and patients with preexisting hepatic encephalopathy or neurologic disease may be at increased risk for this complication. The mainstay of treatment is tacrolimus dose reduction or discontinuation, although benzodiazepine therapy may be beneficial in the treatment of this disorder. Clinicians should be aware of the potential adverse effects associated with calcineurin inhibitor toxicity in transplant patients and should advocate for aggressive and rapid treatment of this serious adverse drug effect.