The impact of vasculitis as a cause of primary rapidly progressive crescentic glomerulonephritis (RPGN) was examined in patients with Thai ethnic by antineutrophil cytoplasmic antibody (ANCA) test. Thirty patients found in a six years study period were included. Patients' mean age was 34.8+/-16.4 years. Mean crescent score was 86.2+/-22.9%. ANCA proved positive in fifteen patients. This helps to differentiate vasculitis associated (ANCA positive) from nonvasculitis (ANCA negative) RPGN. Incidence of immune complex type RPGN (46.6%) is higher than the Caucasians while the incidence of antiglomerular basement membrane antibody (anti-GBM disease) is much lower. More vasculitis patients were treated with cyclophosphamide (n = 11) than the nonvasculitis group (n = 2). Mean renal survival time of ANCA and non-ANCA associated patients were 26.69 and 14.16 months, respectively. Renal survival of all patients is significantly worse if associated with a high entry creatinine (>6 mg/dl). Our results show that vasculitis associated RPGN is not an uncommon disease in the Thai population and can be recognized initially by ANCA test.