There is a well documented risk of late infection following both splenectomy and bone marrow transplantation. In asplenic patients, the phagocytic and antibody producing roles of the spleen are lost and there is a lifelong susceptibility to infection which may be overwhelming and fatal. Patients most at risk are children, those with underlying lymphoproliferative disorders and those receiving immunosuppressive therapy. Although it is hard to prove benefit from preventative strategies, patients are likely to benefit from prophylactic antibiotic therapy and from immunisation with pneumococcal, Haemophilus influenzae-B and meningococcal vaccine given prior to splenectomy. Following an allogeneic bone marrow transplant (BMT), recovery of immune function takes up to a year. During this time, patients are at high risk from cytomegalovirus (CMV) and varicella zoster virus (VZV) infections and also from pneumocystis pneumonia. Prophylactic medications are used to good effect. The major threat of late infection occurs in patients with chronic graft versus host disease (cGVHD)--there is increased susceptibility to bacterial, fungal and viral infections. Many patients without cGVHD recover immune function fully and many develop antibodies to specific recall antigens. This does not occur in all patients and although there is a low risk of infection with organisms against which vaccines are available. If it is not possible to measure specific antibody titres and consequently offer selective re-immunisation, then a universal vaccination strategy should be in force. Response to vaccines is likely to be poor before one year post BMT. For autologous transplant recipients, immune recovery is probably complete and routine re-immunisation is not likely to offer much benefit. For both asplenic and bone marrow transplant patients, education of patient and physician is important.