We analysed the records of 44 paediatric cases of acute haematogenous osteomyelitis (age 0-14 years) and 25 cases of purulent arthritis (age 0-13 years). The annual incidences were 4.5 and less than two per 100,000 children, respectively. Bacteriologic diagnosis was achieved in 82% of the acute haematogenous osteomyelitis cases and in 40% of the acute purulent arthritis cases. Staphylococcus aureus was responsible for 70% of the proven acute haematogenous osteomyelitis and acute purulent arthritis cases combined, followed by streptococci (20%) and Haemophilus influenzae (7%), which caused only acute purulent arthritis. Acute haematogenous osteomyelitis was localized in the femur in 41% of the cases and acute purulent arthritis in the knee joint in 76%. Surgery (in most cases drilling, fenestration or arthrotomy) was performed on 82% of the acute haematogenous osteomyelitis and on 32% of the acute purulent arthritis patients. Although six of the acute haematogenous osteomyelitis patients (but none of the acute purulent arthritis patients) underwent surgery for a second time, permanent damage, which was functionally non-significant, developed in only 14%. No sequelae were found in the acute purulent arthritis group. The average duration of antimicrobial therapy was 44 days in the acute haematogenous osteomyelitis group and 29 days in the acute purulent arthritis group. The prognosis for the children was similar, irrespective of whether the drugs used were staphylococcal penicillins, ampicillin, lincomycin or clindamycin.