The increasing use of hematopoietic stem-cell transplantation (HSCT) for the treatment of leukemia and lymphoma has subjected patients with these diseases to a variety of neurologic complications, some of which have been described only in the transplant population. Neurologic complications differ in patients receiving autologous versus allogenic HSCT, and the spectrum of possible complications changes during the course of HSCT. Neurologic complications of HSCT are frequently serious, difficult to diagnose and treat, and a source of considerable morbidity and mortality. Knowledge of possible explanations for neurologic symptoms and signs in patients receiving HSCT can accelerate an accurate diagnosis and timely therapeutic intervention.