Direct observations of the surfaces of orthopaedic prostheses that have failed and of bone affected by osteomyelitis with and without the presence of a prosthesis have shown that the bacteria that cause these infections live in well-developed biofilms. The cells within these matrix-enclosed surface-associated communities are protected from host defenses and antibiotics, and clinical experience has shown that they must be removed physically before the infection can be resolved. The biofilm etiology of these diseases demands new diagnostic methods because biofilm cells typically do not grow on agar plates when recovered by scraping or swabbing. I will recommend new molecular and immunologic diagnostic methods that have been useful in other biofilm infections. These diseases progress through quiescent periods that alternate with acute exacerbations, and clinicians must realize that antibiotic therapy can control the acute phases but cannot resolve the basic biofilm nidus of the infection. Now that it has been realized that these orthopaedic infections are caused by relatively common biofilm-forming bacterial pathogens, new technologies that deliver very high concentrations of antibiotics locally and "on demand" and novel molecular "mimics" that block the signals that control biofilm formation need to be examined.