Osteoarthritis of the hip is rapidly progressive in 5% of cases, particularly in patients of advanced age. At times there is total destruction of the femoral head. Nineteen such cases are described and the literature is reviewed. The clinical picture is dominated by rapidly progressive pain and limping; the radiographic picture by the absence of osteophytosis. The pathology of rapid progression is subdivided into primary and secondary. Several hypotheses of the pathogenesis are discussed. These are related to mechanical overloading factors, local cortisone therapy, anoxia, synovitis. Differential diagnosis is with subacute septic arthritis, monarticular rheumatoid arthritis, and idiopathic osteonecrosis of the femoral head. Prosthetic replacement is the only treatment indicated and the long-term results do not differ from those obtained in prosthetic replacement for the more common type of osteoarthritis.