Overwhelming postsplenectomy infection (OPSI) due to group B streptococcus developed in an insulin-dependent diabetic patient. The illness began with nonspecific symptoms, followed rapidly by hypotension and disseminated intravascular coagulation. The early institution of appropriate antibiotics, fluid replacement and pressor agents resulted in a favorable clinical outcome. The association of group B streptococcal infection and diabetes mellitus is discussed. The defects in normal host defenses associated with asplenic state and diabetes mellitus are further emphasized. This is the first case report linking the association of OPSI, diabetes mellitus and group B streptococcal septicemia.