Sixty children younger than 3 years with culture-positive hematogenous septic arthritis and acute/subacute osteomyelitis treated between 1990 and 1995 were reviewed to identify the infecting organism. Gram-positive bacteria were identified in 47 (78.3%) patients, and gram-negative organisms were identified in 13 (21.7%) patients. Haemophilus influenzae was cultured in none of the cases of septic arthritis and in only one (1.6%) case of acute osteomyelitis. Kingella kingae was cultured in 10 (16.7%) cases, with all of these patients between the ages of 10.5 and 23.5 months. Routine immunization of infants against H. influenzae has caused a change in the historically reported bacteria of bone and joint infections in children younger than 3 years. Haemophilus influenzae has lost its predominance as the most commonly identified gram-negative pathogen, and in this study, has been replaced by K. kingae.