During a six-year period, 17 patients younger than 20 years of age, with a final diagnosis of subacute osteomyelitis, were admitted to the Norwegian Radium Hospital because of an initial suspicion of primary malignant bone tumour. The most common localizations were the metaphyses of long bones (eight patients) and the clavicle (four patients). Pain was the dominating symptom. Common radiological findings were localized osteolysis and/or sclerosis, cortical bone destruction, periosteal reaction and an adjacent, often palpable soft tissue mass. Clinical signs of infection were generally absent, and a positive bacterial culture was obtained from the biopsy material in only one patient. Following extensive investigations, a malignant bone tumour (especially Ewing's sarcoma) remained a differential diagnosis, and open biopsy was indicated in all cases. The patient material illustrates the difficulty in distinguishing between subacute osteomyelitis and malignant bone tumours, and it is stressed that diagnostic investigations for this type of patients should be performed in an oncological centre with experience of bone tumours.