A retrospective analysis of the records of 46 patients with adult-onset mesangiocapillary glomerulonephritis seen over a period of 15 years is reported. There were 28 males and 18 females with a mean age of 34 years. Mean observation period was 60 months. All patients had renal biopsies and characteristic changes, but no dense deposit variant was seen. HBsAg was positive in 20 per cent of the patients tested whereas in the general population it was about 10 per cent. Nephrotic syndrome was the commonest presentation. There was a mean delay of 8.5 months between the onset of symptoms and renal biopsy. Nineteen patients were given steroid/immunosuppressive therapy while 27 received no specific treatment. At the time of review, renal function was stable in 13 patients but progressively deteriorating in 33. In the latter, the slope of the graph of reciprocal of creatinine versus time could be accurately determined. Steroid/immunosuppressive therapy did not influence the rate of progression of renal failure but appeared to hasten and induce more partial remissions of the nephrotic state. There was no difference in cumulative renal survival between treated and untreated patients, and between HBsAg-positive and negative patients. Overall, 23 patients required dialysis/renal transplantation and an additional four had died of end-stage renal failure at the time of this review.