We aimed to calculate the annual incidence of Wegener's granulomatosis (WG) in Norfolk (UK) and to compare the clinical spectrum of disease to that seen in tertiary centres in both the UK and USA. We also aimed to examine the seasonal onset of symptoms. This was a prospective study of all patients presenting with WG to a district hospital with a well-defined stable population (515,000) during the period 1988-1993. The annual incidence for WG in the adult population is 8.5/million (95% CI 5.2-12.9). These are the first incidence figures for a well-defined population and are higher than previously published. The clinical spectrum of disease in Norfolk was similar to that seen in tertiary centres and there is supportive evidence for a seasonal variation in the onset of symptoms (highest in winter).