Septic arthritis is a direct invasion of the joints by pathogenic micro-organisms. These micro-organisms and their products stimulate the release of pro-inflammatory cytokines and proteolytic enzymes that induce an inflammatory response and degradation of the cartilage. Staphylococcus aureus remains the most prevalent micro-organism, and the most important aetiological change has been the decreased incidence of gonorrhoea, which is related to changes in sexual behaviour as a result of the HIV epidemic. Diagnostic suspicion is based on clinical symptoms, imaging findings and examination of synovial fluid. Scintigraphy and magnetic resonance imaging are useful methods for localizing and defining the extent of infection. The definitive diagnosis is based on the isolation and culture of the pathogen from synovial fluid. Optimal cultures are obtained by inoculating the synovial fluid immediately into blood culture bottles. Treatment includes initial empirical antibiotics, which are modified according to the synovial fluid culture. It is recommended that 3-4 weeks of intravenous antibiotic therapy are followed by 2 or 3 more weeks of an oral regimen. Adequate drainage may be performed by means of repeated needle aspiration, arthroscopy or surgery. Recent studies on the pathogenic mechanisms of septic arthritis have led to the simultaneous use of intra-articular steroids and antibiotics in order to reduce articular damage.