Multicentric Castleman's disease (MCD) is a rare lymphoproliferative disorder found with a higher frequency in HIV-seropositive patients. Human herpes virus 8 is found in virtually all cases of HIV-associated MCD. The majority of cases of MCD in patients with HIV are also associated with Kaposi's sarcoma. The dysregulated production of human IL-6 is thought to be an important factor in the pathogenesis of MCD. HIV-seropositive individuals with MCD have a significantly greater risk of developing non-Hodgkin lymphomas than their HIV-seronegative counterparts. MCD occurring in HIV patients has been associated with a poor prognosis. With newer therapy regimens, it is hoped that the prospects of HIV-infected patients with MCD will improve.