Background: Acute haematogenous osteomyelitis is a bacterial infection of bone, which occurs most frequently in children. Outcomes are excellent for the majority of children, but a minority develop complicated osteomyelitis. Predicting which children will develop complicated osteomyelitis remains a challenge, particularly in developed countries where most patients are discharged home after a relatively short period in hospital. Methods: We conducted a 5-year retrospective case note review of all children aged 3 months to 16 years admitted with a diagnosis of acute haematogenous osteomyelitis. We compared standardized clinical and laboratory parameters in those who developed simple and complicated osteomyelitis. Results: Of the 299 children who met inclusion, 241 (80.6%) had simple and 58 (19.4%) had complicated osteomyelitis. The major predictors of complicated disease were older age, a temperature greater than 38.5°C and a higher C-reactive protein at admission. Conclusions: A risk prediction model, utilizing information available shortly after hospitalization, allows early identification of children at greatest risk of developing complicated osteomyelitis.