Fever of unknown origin (FUO) is a problem frequently faced by clinici
ans all over the world. One hundred and twenty-one cases of FUO presen
ting 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 c
ommonest infection encountered. Collagen vascular diseases and tumours
accounted for 15.7 and 8.3% cases, respectively. No cause could be fo
und out in a substantial number of cases (19%) even after invasive inv
estigations. Knowledge of the current patterns of FUO is important sin
ce many patients present with potentially treatable diseases.