The authors report the data collected by a national investigation organized by the French Society of Rheumatology, concerning the osteo-articular manifestations of severe acne, palmo-plantar pustulosis and primary thoracic and peripheral hyperostosis. This investigation collected 85 case-reports including 13 severe acne, 44 PPP and 28 hyperostosis without the dermatitis mentioned above. From this investigation, it appears that dermatological and osseous pictures described under various denominations, present common characteristics and transition forms justifying their common study under the acronym SAPHO (Syndrome Acne-Pustulosis-Hyperostosis-Osteitis). The bony involvement, especially anterior thoracic, but also vertebral and even peripheral seems to be the common denominator between these diseases. It realizes a true rheumatoid inflammatory osteitis, osseous counterpart of synovial and cartilagenous affections in inflammatory rheumatoid diseases. This group has rather loose connections with common psoriasis and slightly more definite relationships with primary ankylosing spondylarthritis. These clinical and immunogenetic connections occur also through bony involvement.