The outcome of bacterial arthritis is generally poor: the mortality is 10-15% and there is loss of joint function in 25-50% of the survivors. Adverse prognostic factors are advanced age, a pre-existent joint disease and an infection of a prosthetic joint. The incidence of bacterial arthritis is low: 2-6 per 100,000 persons per year. Risk factors are advanced age, a joint disease--especially rheumatoid arthritis--diabetes mellitus and presence of a prosthetic joint. Situations that can lead to bacterial arthritis are mainly skin infections of the feet and only rarely invasive medical or dental procedures. Because of the severity of the disease, antibiotic prophylaxis of haematogenous bacterial arthritis in patients with prosthetic joints is advocated in guidelines. However, because of the rarity of the disease it is unclear whether the advantages of prophylaxis outweigh the disadvantages of the large-scale use of antibiotics, such as side effects, costs and increased resistance of bacteria. In a decision analysis of a large group of patients with joint diseases, antibiotic treatment of skin infections appeared to be (cost-)effective in the prevention of haematogenous bacterial arthritis, mainly in high-risk patients. On the other hand, prophylaxis around medical or dental procedures was not (cost-)effective, except possibly in a small group of patients with increased risk.