We studied the clinical features, blood levels of cyclosporine, and neuroimaging findings in 46 patients with cyclosporine neurotoxicity after liver transplantation. The clinical presentation of cyclosporine neurotoxicity was characterized by tremulousness and restlessness in all patients and was associated with acute confusional state and psychosis in 20 patients, seizures in eight, speech apraxia or action myoclonus speech in three, and cortical blindness in two. In 35 patients, cyclosporine neurotoxicity occurred during IV treatment. Neuroimaging studies showed only minor white matter abnormalities in two patients despite dramatic clinical presentations, including speech difficulties, seizures, and cortical blindness. In only 19 of 31 patients (61%) did trough levels of cyclosporine suggest neurotoxicity. Neurologic findings were reversible in all patients after cyclosporine was withheld and then given in lower dosage. In three patients, substituting FK 506 did not result in neurotoxicity.