Periprosthetic infection is a permanent risk and severe complication in joint arthroplasty. Systematic diagnostics under optimal conditions are necessary for a successful therapy. Patient history, clinical examination and an elevated CRP-level is the basis for suspicion of infection. The diagnosis is confirmed by identification of the pathogen from a sample collected through joint aspiration under sterile conditions. The microbiological examination is done in a laboratory specialized in the diagnosis of foreign body infections. The pattern of resistance of the identified pathogen determines the topical and systemic course of antibiotics. Surgical treatment is characterized by exchange of the prosthesis and radical debridement. The exchange can be carried out in one or two stages. The one-stage exchange offers several advantages compared to two or more stage procedures for all those involved - patient, surgeon and health care system - while providing the same chance of successful elimination of infection, with even better functional results.