Osteomyelitis (OM) is an infection of bone. Symptoms may include pain in a specific bone with overlying redness, fever, and weakness. The long bones of the arms and legs are most commonly involved in children e.g. the femur and humerus, while the feet, spine, and hips are most commonly involved in adults.

The cause is usually a bacterial infection, but rarely can be a fungal infection. It may occur by spread from the blood or from surrounding tissue. Risks for developing osteomyelitis include diabetes, intravenous drug use, prior removal of the spleen, and trauma to the area. Diagnosis is typically suspected based on symptoms and basic laboratory tests as CRP and ESR.This is because plain radiographs are unremarkable in the first few days following acute infection. This is then supported by blood tests, medical imaging, or bone biopsy.

Treatment of bacterial osteomyelitis often involves both antimicrobials and surgery. In those with poor blood flow, amputation may be required. Treatment of the relatively rare fungal osteomyelitis as mycetoma infections entails antifungal medications. In contrast to bacterial osteomyelitis, amputation or large bony resections is a more common fate of neglected fungal osteomyelitis namely mycetoma where infections of the foot account for the majority of cases. Treatment outcomes of bacterial osteomyelitis are generally good when the condition has only been present a short time. About 2.4 per 100,000 people are affected a year. The young and old are more commonly affected. Males are more commonly affected than females. The condition was described at least as early as the 300s BC by Hippocrates. Before the availability of antibiotics the risk of death was significant.