AIMS: To measure the time between onset of symptoms and intention to treat in patients with anti-neutrophil cytoplasmic antibody (ANCA) associated glomerulonephritis; and to investigate the effect of any delay in diagnosis on disease severity at presentation and outcome. METHODS: All ANCA positive patients with biopsy proven glomerulonephritis presenting in the North West Region over a consecutive period of 57 months were identified from the North West Glomerular Disease Registry. Sixty nine patients were identified and notes from 61 were reviewed. RESULTS: The 61 patients had a median diagnostic delay of 92 days. In only 12 patients had an ANCA test been performed prior to the nephrology referral. Thirty three patients had renal failure requiring dialysis within one week of admission and had a shorter delay (median 72 days) than those not requiring dialysis (median 132 days). None of the 28 patients with independent renal function at presentation required dialysis subsequently. Eighteen (55%) of those who required dialysis recovered independent renal function at three months and 13 (39%) had long term recovery. Both for patients who did and did not undergo dialysis, a longer delay was correlated with an increased percentage of sclerotic glomeruli at presentation. Patients with end stage renal failure had a median delay of 92 days, compared with one of 42 days in those who were dialysis independent at final follow up. CONCLUSIONS: Prolonged delay in diagnosis of ANCA associated glomerulonephritis is associated with an increased risk of end stage renal failure.