Clinical data in 244 patients with IgA nephropathy and biopsy findings in 519 biopsies (107 patients had at least two biopsies) were analysed. Males predominated (73 per cent) and had more severe disease and a worse prognosis than females. The most frequent symptom was macroscopic haematuria, often with associated loin pain; however, this was typical only in young males. Hypertension was the major presenting feature in 23 per cent of patients. Urinary erythrocyte counts correlated with the presence of crescents on biopsy (p less than 0.0001). Serum IgA levels wer elevated in only 21 per cent, while IgM levels were raised in 43 per cent of patients. Two hundred and seventeen patients were followed for at least one year (mean 59.7 months, range 12-255 months). In 82 patients five-year follow-up and in 33 patients ten-year follow-up data were available. Five- and 10-year survival figures were 91.5 and 87.5 per cent respectively. Clinical resolution occurred in only 6 per cent of patients but in those who had biopsies following clinical resolution, diffuse mesangial cell proliferation and IgA deposits persisted in all. The rate of clinical deterioration correlated with proteinuria, hypertension, impaired renal function, crescents and sclerosed glomeruli on biopsy. Continuing high urinary erythrocyte counts were the strongest predictor of a progressive course.