Chronic lymphoplasmacellular osteomyelitis may occur in children, adolescents and adults, but has not been found in newborns or babies either in our series or in the literature. Symptoms suggesting an acute disease like fever are uncommon, but a primary chronic course with symptomatic and asymptomatic periods is typical. Pain and swelling are the main symptoms; painless masses are rare. In children and adolescents the clavicle and metaphyseal regions of long bones are typical sites of chronic abacterial osteomyelitis. In adults the clavicles or the first two ribs are mainly affected with synovitis of the adjacent joints, but the long bones are rarely involved. Laboratory findings are non-specific but important for the differential diagnosis. The sedimentation rate and c-reactive protein might be elevated. The X-ray examination shows osteolytic, sclerotic or mixed bony changes and, in case of a diaphyseal involvement, onionskinlike periosteal bone formation may be present, suggesting a malignant process. In late stages sclerotic bone formations may be seen as a rest. Uni- or multifocal lesions can be detected by bonescan, as can asymptomatic lesions. Magnetic resonance imaging shows gross signal intensity differences both in the bone and perifocal soft tissue and involvement of the synovium with gadolinium DPTA enhancement in T1-weighted images. In early stages of the disease granulocytes, microabscesses and new bone formations might suggest bacterial osteomyelitis that cannot be differentiated by histology. In intermediate phases lymphocytic and plasma-cellular infiltrates are found, whereas in late phases sclerotic bone formations and fibrosis of the bone marrow are seen histologically. In chronic lymphoplasmacellular osteomyelitis, all clinical, radiological and histological findings, as well as negative bacteriological cultures, are mandatory and will allow a definitive diagnosis to be made. The disease may be uni- or multifocal, and new bone lesions may occur over time, as well as skin manifestations, which can be found years before or after bone involvement. The association with dermatological diseases and/or synovitis led to the acronym SAPHO syndrome (synovitis, acne, pustulosis, hyperostosis, osteomyelitis). For the treatment nonsteroidal anti-inflammatory drugs are effective for pain relief, reduction of swelling and dysfunction. Antibiotics have been used in several series and are not effective. Major surgery is not recommended even for recurrences, and the prognosis for growth and function is excellent in the long term despite recurrences over several years.