We studied the etiology, treatment, death rate, and the stage of disease of the HIV infected patients admitted to our ward with fever of unknown origin (FUO). Most of the studied patients were in the last stage of the HIV infection, the number of CD4 lymphocytes was low. FUO was caused by mycobacteria in >50% of the cases, but we had cases of drug fever, lymphomas, and fever caused by the HIV infection itself. In most of the cases empiric antituberculous therapy was begun, this was successful in >50% of the cases. Conclusions: FUO appeared especially in patients in the last stage of HIV infection who had no antiretroviral therapy before, with a high death rate in this group. All possible opportunistic infections must be treated in these patients and the antiretroviral therapy must be started.