Pauci-immune crescentic glomerulonephritis (PICGN) is a rapidly progressive condition leading to renal failure within days or weeks and is potentially life threatening. Majority of these patients have clinical or pathological evidence of systemic vasculitis. PICGN may occur as renal limited disease or as a component of systemic necrotising small vessel vasculitis. Majority of these cases are attributed to Wegener's granulomatosis (WG), microscopic polyangitis (MPA) or Churg Strauss syndrome (CSS). Renal involvement is encountered in 80 to 90% cases of WG and MPA and in about 45% cases of CSS. Approximately 80 to 90% patients of untreated WG or MPA and about 60% cases of CSS are positive for anti-neutrophilic cytoplasmic antibodies (ANCA). These diseases are therefore also called as ANCA-associated vasculitis. Serial ANCA measurements provide useful information on disease activity. Renal transplant should be avoided in patients with clinical evidence of active vasculitis. Even though the treatment with oral corticosteroids and i.v. or oral cyclophosphamide results in complete long term remission in 70 to 75% patients, relapse occurs in >25% cases within a mean period of 18 months after cessation of therapy. Prognosis of untreated ANCA-associated PICGN is poor.