During a seven-year period (1986-1992) 719 adults (age > 16 years) underwent diagnostic renal biopsy in Stockholm (adult population 1.2 million). Seventy-one (10%) new cases of pauci-immune necrotizing and crescentic glomerulonephritis (NCGN) with or without systemic vasculitis were found: 39 females and 32 males (median age 67, range 20-84 years). The mean yearly incidence for the whole period was 0.8/100,000 population. The yearly incidence doubled from 0.6 before to 1.2/100,000 population after 1990. The incidence was highest among those > 65 years of age. Age-corrected incidences for this age group increased from 1.4 before to 3.9/100,000 after 1990. Anti-neutrophil cytoplasmic antibodies (ANCAs) tested in 60, showed antibodies against proteinase 3 (PR3) in 29 patients, against myeloperoxidase (MPO) in 26 and none in five patients. Mortality was highest in the early stages of the disease. From a total of 11 patients, 7 (15%) died within 2.5 months of diagnosis. Forty-six out of all 71 patients with NCGN belonged to the catchment area of our clinic and were studied in more detail. Twenty-six had microscopic polyangiitis (ANCAs were analyzed in 24, of these 16 had anti-MPO, 6 anti-PR3, 2 had none), 13 had Wegener's granulomatosis (ANCAs were analyzed in all, of these 12 had anti-PR3, 1 anti-MPO) and seven had disease limited to the kidneys (ANCAs were analyzed in 6, 5 had anti-MPO, one was negative). At the time of diagnosis, 16 patients had s-creatinine < 300 mumol/l while 14 patients were dialysis-dependent (seven only temporarily). All patients received immunosuppressive therapy.(ABSTRACT TRUNCATED AT 250 WORDS)