The use of leukodepleted cellular blood components may reduce some adverse effect of transfusion in certain indications. This review presents the adverse effects of contaminating donor leukocytes in blood components: alloimmunisation, febrile nonhemolytic transfusion reactions, refractoriness to platelet transfusions, graft versus host disease, transmission of leukotropic infections and immunomodulation. The value of leukodepletion in preventing some of these complications, methods of leukodepletion and the current indications of use of leukodepleted components in clinical practice are discussed.