Three children had osteomyelitis due to Haemophilus influenzae type b. They were seen with signs and symptoms indistinguishable from infection caused by other organisms. One child was initially misdiagnosed as having septic arthritis because of failure to appreciate that Hemophilus may also cause bone infection. In the second patient osteomyelitis and arthritis developed during ampicillin sodium therapy for treatment of Hemophilus meningitis. His initial infection was caused by an ampicillin-sensitive isolate but his orthopedic infection subsequently responded to therapy only after changing to a regimen of chloramphenicol. In the third patient, bone scintigraphy was helpful in diagnosis since serial roentgenograms were not diagnostic of osteomyelitis. The anticapsular antibody responses of these patients were measured by radioimmune assay. The levels found were low but comparable to age-matched control children with H influenzae type b meningitis.