Mediastinal germ cell tumours (GCT) carry a poor prognosis, particularly after relapse. We have reviewed the published reports of current treatments and describe a case with a cure after an allogeneic bone marrow transplant, which is not reported in the current published data. We believe that GCT may be susceptible to a graft-versus-tumour effect and suggest that patients with relapsed GCT be considered for allogeneic transplantation.