Twenty-nine uremic patients with fever of unknown origin (FUO) admitted to our clinic between 1994 and 1998 were evaluated prospectively. A group of 50 consecutive non-uremic patients with FUO followed up during the same period was used for comparison. The causes of FUO found in the uremic and non-uremic groups, respectively were as follows: infectious diseases, 69 vs. 44% (p = 0.03); collagen vascular diseases, 6.9 vs. 6%; neoplasms, 3.4 vs. 26%; miscellaneous causes, 3.4 vs. 16%; and undiagnosed, 17.2 vs. 8%. Tuberculosis was the most common cause of FUO in both groups. The spectrum of underlying conditions for FUO in our uremic patients differed from that in the non-uremic patients and the uremic patients had a very high propensity for infectious diseases, especially tuberculosis.