Relapse of peripheral non-Hodgkin's lymphoma (NHL) in the central nervous system commonly has a poor prognosis. Graft-versus-leukemia effects (GvL) contribute substantially to eradication of hematological malignancies after allogeneic stem cell transplantation. Few data are available describing GvL activity within the brain. We report the case of a man allografted for peripheral NHL. On day +83 after transplantation a CNS relapse of the lymphoma occurred. The brain was irradiated with 44 Gy, anti-CD20 antibodies were given, and the immunosuppression was withdrawn. Subsequently, limited-stage, chronic graft-versus-host disease occurred. The lymphoma regressed completely, and the patient has been in continuous complete remission for 30 months. The favorable course suggests substantial contribution of immunomodulation to excellent outcome.