Osteomyelitis is a non‐specific infection of the bone and bone marrow. In the past acute osteomyelitis (AO) led to high mortality especially in non‐adults. Nevertheless, its diagnosis in archaeological populations is rare. Documented individuals with known cause of death offer a unique opportunity to study this condition. This article aims to describe the bone lesions in non‐adults diagnosed with AO at the Coimbra University Hospital (CUH) and now belonging to the Coimbra Identified Skeletal Collection (CISC). Moreover, mortality rates and demographic profiles for individuals aged ≤18 years old and diagnosed with AO in the CUH, between 1923 and 1929, were also determined. The 5 (1%) non‐adults in the CISC with AO listed as cause of death were selected for this study, and their bones were analysed macroscopically and radiologically. The skeletal remains of one individual revealed a small area of new bone formation in the shaft of the left femur. Radiography of this bone showed a radio‐opaque area in the diaphysis. The other four individuals show evidence of surgical treatment, responsible for many cases of disability in the past. In the 7‐year period under analysis, 122 juveniles were diagnosed with osteomyelitis and admitted for surgery at the CUH, 43 (35.2%) of which were diagnosed with AO. Sixty‐five per cent of the cases of AO occurred between the ages of 8 and 15 years, with boys twice as frequently affected as girls, and lower limb bones were involved in 91% of AO cases. AO was responsible for 76.9% of the deaths. This study of pre‐antibiotic non‐adults may help to recognize skeletal signs of AO and their surgical treatment in unidentified skeletal remains. Copyright © 2012 John Wiley & Sons, Ltd.