Both acute and chronic osteomyelitis are causes of rising concern, mainly because of the increasing number of traumatic accidents, the appearance of new groups of patients at risk, the widespread use of prosthetic devices and the emergence of new patterns of antimicrobial resistance. Classification systems, clinical features and risk factors will be reviewed. Diagnosis is usually clinical and microbiological, but imaging techniques such as plain radiography, radionuclide imaging, computed tomography and magnetic resonance imaging are commonly used. Decisions regarding the best imaging modality can be challenging and should reflect the location of the suspected infection and any associated illnesses or bone disorders. Osteomyelitis is characteristically recurrent, needs multiple surgical interventions and is resistant to short courses of therapy. The application of more precise diagnostic techniques and the availability of non-toxic, highly efficacious oral antimicrobial agents frequently permit a long-term ambulatory approach. The optimal length of therapy has not been established.