Summary. Calcineurin inhibitor-induced central nervous system toxicities are uncommon and often resolve after discontinuation of the offending drug. The long-term outcome of these patients is, however, unknown. Resolution of symptoms occurred in 70% of 30 allografted recipients who developed calcineurin inhibitor-induced neurotoxicity. When patients were rechallenged with the same or a different calcineurin inhibitor, symptoms recurred in 41%, leading to permanent discontinuation of the drug. De novo or progressive acute graft-versus-host disease (GVHD) was observed in 54% of patients at a median of 7 d (range 1–70 d) after initial onset of neurotoxicity. The prognosis was grim, with 24 (80%) of these patients dying a median 33 d after the onset of neurotoxicity (range 2–594 d). GVHD and/or infection occurred in 54% and were the most common primary causes of death. We conclude that calcineurin inhibitor-induced neurotoxicity is frequently reversible but associated with a poor prognosis.