Chronic non-bacterial osteomyelitis (CNO) is an autoinflammatory disease with unpredictable, painful courses of osteolytic lesions in the bones. CNO is frequently associated with psoriasis and inflammatory bowel disease. In cases with multifocal lesions the term chronic recurrent multifocal osteomyelitis (CRMO) is preferably used. SAPHO (synovitis, acne, pustulosis palmoplantaris, hyperostosis and osteitis) syndrome is regarded as CRMO in adults. New knowledge of the hereditary forms like Majeed syndrome, deficiency of IL-1-receptor antagonist and cherubism is described.