Fever of unknown origin (FUO) was described by the criteria of Petersdorf and Beeson, and the aetiology includes primarily infectious, collagen-vascular, and neoplastic diseases. The distribution of the disorders causing FUO may differ according to the geographic area and the socioeconomical status of the country. Moreover the developments in radiographic and microbiologic methods have changed the spectrum of diseases causing FUO. In this study, we reviewed 117 cases fulfilling the criteria of FUO followed in our unit between 1984-2001. In 34% of the patients with FUO, the aetiology was infectious diseases, in 23% collagen vascular diseases, in 19% neoplasms, and in 10% miscellaneous diseases. In 14% of the cases the aetiology could not be found. Three leading diseases were tuberculosis (24%), lymphomas (19%), and Still’s disease (11%). The study reports tuberculosis as a more frequent cause of FUO than the other FUO series reported from the developed countries. Invasive procedures helped to establish the diagnosis in 50 out of 92 patients (43%). As a final diagnostic procedure, laparotomy contributed to the establishment of the diagnosis in 15 out of 20 patients (75%).In our country, infectious diseases and especially tuberculosis is a more frequent cause of FUO. Beside infectious diseases, collagen-vascular and neoplastic diseases should be considered in the differential diagnosis of a patient admitted with FUO.