Hematologic and immunologic changes following splenectomy for trauma include abnormal RBC morphology, leukocytosis, thrombocytosis, impaired clearance of blood-borne particulate antigens, and reduced antibody formation. These abnormalities may be the bases for overwhelming bacterial infection, the most serious delayed complication of splenectomy for trauma. The state of knowledge at present indicates that splenectomized patients should receive pneumococcal vaccination, but whether penicillin prophylaxis should be given daily in addition is less clear. However, penicillin may be advisable for young children, particularly those under 2 years of age, in whom the efficacy of pneumococcal vaccine has not been established. To prevent sepsis, various surgical alternatives to total splenectomy have been proposed, including deliberate autotransplantation of splenic tissue at the time of splenectomy.