Fever of unknown origin (FUO) is a problem frequently faced by clinicians all over the world. One hundred and twenty-one cases of FUO presenting to a large teaching hospital in northern India were prospectively studied over a period of 2 years. Infections were the commonest cause accounting for 43.8% cases of FUO, with tuberculosis (TB) being the commonest infection encountered. Collagen vascular diseases and tumours accounted for 15.7 and 8.3% cases, respectively. No cause could be found out in a substantial number of cases (19%) even after invasive investigations. Knowledge of the current patterns of FUO is important since many patients present with potentially treatable diseases.