In a retrospective analysis of 2110 admissions to the pediatric intensive care unit, 564 cases of septic shock were identified (26.7% of the total admissions). Septic shock was defined in patients with: (1) clinical evidence of sepsis; (2) fever (greater than 38.3 degrees C) or hypothermia (less than 35.6 degrees C); (3) tachycardia; (4) tachypnea; and (5) inadequate organ perfusion. Inadequate perfusion was defined as hypotension or evidence of peripheral hypoperfusion (poor capillary refill or cyanosis with hypoxemia, oliguria, acidosis or altered mentation). Inotropic support was required to maintain an adequate blood pressure and perfusion in 268 of 564 patients (47.5%). Septic shock with confirmed bacterial infection occurred in 143 patients (143 of 564, 25.2%); these cases were caused by Haemophilus influenzae, type b (59 of 143, 41.3%), Neisseria meningitidis (26 of 143, 18.2%) and Streptococcus pneumoniae (16 of 143, 11.2%). Eight of 564 (1.4%) cases of septic shock were not clinically apparent on initial evaluation and were diagnosed within 24 hours after admission to the hospital. We conclude that septic shock occurs more frequently in children than previously appreciated and may develop after admission to the hospital.