One hundred and twenty-three patients with human immunodeficiency virus infection have been referred to rheumatologists at our hospitals between October 1985 and April 1989 because of musculoskeletal symptoms. Thirty-four homosexual men presented with acute, peripheral, non-erosive arthritis (mean number of four joints affected) with the knees being involved in 23. Other features developing concurrently with arthritis included psoriasis, keratoderma blenorrhagica, plantar fasciitis, urethritis, conjunctivitis and anterior uveitis. Four of five patients investigated were HLA-B27-positive; none of 15 patients tested had raised titres of rheumatoid or antinuclear factors. Various infections were associated with the onset of arthritis and two patients with a recent history of diarrhoea had serological evidence of yersinia infection. No micro-organisms were identified within the joint except for HIV itself. At the time of onset of arthritis four of these individuals had the acquired immunodeficiency syndrome (AIDS); 11 were not known to be HIV-positive before testing which was performed following referral for arthritis. Six patients have since developed AIDS and four have died. In 15 individuals, including those who progressed to AIDS, joint symptoms have been severe, persistent and poorly responsive to non-steroidal anti-inflammatory drugs. In only five patients has the arthritis been known to resolve. Synovitis has also been seen in two women: in one of these HIV infection was thought to have been acquired through intravenous drug abuse. Other rheumatic lesions included myalgia/myositis, non-inflammatory peripheral arthritis, spinal pain, soft tissue lesions, arthralgia or myalgia of unknown cause and infective lesions including septic arthritis and bony infection due to histoplasmosis and atypical mycobacterial infection. It appears likely that HIV infection is a risk factor for the development of seronegative arthritis and other rheumatic lesions.