In a 3-year study of joint infections, undertaken by the author, bacterial infection of a single joint caused severe lameness in 39 sheep older than 6 months; another 15 sheep had polyarthritis consistent with erysipelas. All cases had proven unresponsive to antibiotic therapy administered by the farmer. A penetration wound was responsible for single cases of septic stifle, shoulder, and fetlock; the remaining 36 cases of single joint infection were presumed to have originated from a bacteraemia. Radiography added little additional information except to reveal origin of infection from a growth plate (five cases), and osteophyte formation and erosion of articular surfaces in neglected cases. Necropsy findings were characterised by pronounced synovial membrane proliferation and, in neglected cases, erosion of articular cartilage. Most infected joints contained only small amounts of a pannus. A single treatment success was achieved with arthroscopy and joint lavage from four cases that had been lame for less than 1 week. Sheep with joint infections that remain lame after an appropriate course of antibiotic treatment should be euthanased for welfare reasons.