AIDS: The diagnosis of a relapsing fever of unknown origin (FUO) in a middle-aged HIV-infected male is discussed. The author notes that many of these fevers occur in HIV-infected and AIDS patients with low CD4 counts who have occult infections or malignancies typical of the early stages of HIV. At later stages of AIDS, virtually any opportunistic infection may present with fever alone. In the case of the middle-aged male who did not have low CD4 counts, the author suggests the use of protocols for evaluating FUO in the absence of AIDS, as well as for the usual HIV-associated diagnoses, before assuming that HIV is the cause of the problem. In this case, the diagnosis was finally found to be Hodgkin's disease, with a delayed diagnosis probably due to seeking a more obvious infection in an HIV-infected patient.